Journal archives for November 2021

November 17, 2021

Could Gleditsia have been made by megafungi as well as megaherbivores?

Among leguminous woody plants, mimosas (Mimosaceae) are far more likely than caesalps (see to be favourite foods of large herbivores. Accordingly, it is mimosas, not caesalps, that tend to possess large spines.

However, the genus Gleditsia ( is exceptional among caesalps (see in the degree to which it looks and acts like a member of the mimosas (

Gleditsia has extremely large spines ( and ( and and
and and, as well as small leaflets, flowers lacking obvious petals, and fruits functionally similar to those of mimosas such as that widespread 'acacia', Vachellia nilotica (

Implicit in this convergence with mimosas is that nutritional modes will have likewise converged: we can expect Gleditsia to be adapted to exploit nutrients recycled in urine and faeces, while at the same time fixing atmospheric nitrogen.

It comes as a surprise, therefore, that Gleditsia not only lacks nitrogen-fixing nodules but is listed as possessing ectomycorrhizae (see These macroscopic fungal root-extensions are rare among mimosas ( and antithetical to the nutritional strategy typical of mimosas.

Because the largest mycorrhizal fungi tend to be associated with the roots of plants unattractive to large herbivores, and to promote nutritional regimes antagonistic to herbivory, Gleditsia presents a puzzle. Is its nutritional strategy really similar to those of caesalps which are neither attractive as food for herbivores, nor spinescent (

If it really is ectomycorrhizal, Gleditsia is unique in combining some of the largest stem-protecting spines and some of the largest root-assisting fungi.

I cannot resolve this question because I have yet to find the original paper reporting ectomycorrhizae in Gleditsia. However, I can further explain spinescence in the context of ectomycorrhizal plants generally.

Spines, thorns and prickles vary greatly in their size, the part of the plant from which they are derived, and their adaptive functions. The large spines of many species of 'acacias' (now genus Vachellia) are derived from stipules (e.g.

The largest spines derived from stipules and stems of dicotyledonous plants serve to control the foraging of the largest herbivores. This control should not be confused with deterrence, because plants with large spines are likely to be promoted by regimes of intense herbivory that recycle nutrients via faeces and urine while retarding competing plants. The function of these large spines is not to prevent loss of foliage as much as to protect the crucial regenerative organs/tissues, such as shoots and cambium, in the interests of plant and herbivore alike.

Spines have been established to occur in several genera of ectomycorrhizal plants, but they are of a different kind, compatible with a nutritional regime marginalising large herbivores.

The boreal conifer Picea (, the Australian pea Gastrolobium (, and several Mediterranean and Californian species of oaks Quercus ( are ectomycorrhizal and possess leaf-spines similar to that familiar plant, holly (

Leaf-spinescent plants are basically different from stem- or stipule-spinescent plants in that the leaves are too sclerophyllous (rigidly fibrous and lignified) to be particularly attractive to herbivores in the first place. They generally occur in ecosystems poor in large herbivores, where the main consumer of plant matter is episodic wildfires ( The spines can be thought of as an extension of the unpalatability of the leaves themselves, rather than a means of collaboration with herbivores as seem in spinescent 'acacias'.

Spinescence in ectomycorrhizal plants can therefore be summarised as follows:

In general, ectomycorrhizal plants lack spines, which is unsurprising because the nutritional regimes to which they are adapted are unsuitable for large herbivores. Those ectomycorrhizal species possessing spines tend to have a form of spinescence (i.e. leaf-spinescence) associated with limited herbivory. The stem-spinescence of Gleditsia is so unusual among ectomycorrhizal plants, and the association of Gleditsia with large herbivores is so obvious, that it calls into question the very claim that Gleditsia possesses ectomycorrhizae.

Posted on November 17, 2021 00:47 by milewski milewski | 9 comments | Leave a comment

November 18, 2021

The puzzle of conspicuous pallor in a Sahelian giraffe, part 1

Does anyone doubt that, in general, the colouration of giraffes is a form of camouflage?

The flags which I have described (see hardly negate this generalisation, because they are subsidiary features.

However, one subspecies of giraffe has overall colouration so conspicuously pale that it does seem to mean a partial negation ( and

I refer to Giraffa camelopardalis peralta ( and and of the western Sahel.

The particular pallor of Giraffa camelopardalis peralta is owing mainly to the breadth of the whitish 'matrix' among the blotches (see and

This differs from any pale overall effect in the form of giraffe inhabiting the edge of the Namib desert in southern Africa, which is owing mainly to fading of the blotches themselves and does not particularly affect the head or legs (Giraffa giraffa angolensis, see and

The following photos of the most pallid individuals show how the camouflage effect has been compromised in Giraffa camelopardalis peralta in its current habitat. Although a corollary of the pallor is that the auricular and pedal flags are reduced, the caudal flag is if anything enhanced, because the tail-tassel remains black in all individuals.

Can it not be said that G. c. peralta has, in evolutionary terms, switched from inconspicuous colouration to conspicuous colouration? The mechanism has been a quantitative shift (mainly an encroachment of the pale matrix relative to the blotching), but the effect seems qualitative.

If so, this seems convergent with the conspicuous pallor of three other gregarious ruminants of the southern fringes of the Sahara, as exemplified by the following views of Oryx dammah: and

Oryx dammah (, Addax nasomaculatus and Nanger dama ruficollis ( all inhabited the vicinity of the Sahara, with O. dammah coexisting in the Sahel with giraffes (including G. c. peralta), A. nasomaculatus penetrating the Sahara itself, and N. d. ruficollis living in the eastern Sahel (where the local form of giraffe was not as pallid). In converging on a pattern of conspicuous overall pallor, these species set an unique pattern among the arid-adapted ungulates of the world.

I realise that:

  • arid-adapted reptiles, birds, and small mammals tend to be pallid as a form of crypsis in the pale environments of deserts, particularly sandy deserts;
  • there is seasonal variation in the colouration of A. nasomaculatus and possibly also the other two bovids referred to here; and
  • hippotragins and gazelles tend to be adaptively conspicuous even in savannas, which can be partly explained by the futility of trying to hide as gregarious animals in the open.

However, ruminants in the southern African deserts and semi-deserts ( and lack the relevant pattern of colouration. In the degree of their pallor, our three bovids seem to have adapted in convergent ways to the particular conditions of the Sahara and its southern edges.

Seen in this context, does the pallor of G. c. peralta not seem to be part of a regional faunistic pattern?

The following illustrate the pallor of our three bovids, and the adaptive convergence that this represents.

Oryx dammah:

Addax nasomaculatus:

Nanger dama:

to be continued...

Posted on November 18, 2021 11:28 by milewski milewski | 5 comments | Leave a comment

November 19, 2021

Reframing the reticulated giraffe

Which iNaturalists would identify the following as the reticulated giraffe? and

I offer this Post in aid of sharpening your search-image.

Everyone knows that a diagnostic feature of the reticulated giraffe (Giraffa reticulata) is the conversion of the normal blotchiness of giraffes into a network effect ( and and

However, several features seem to have been overlooked in the literature (e.g. see and So it may be time to re-define the reticulated giraffe from a broader perspective.

Here we have the most uniformly-coloured and most thoroughly camouflaged of all giraffes ( and

The auricular and caudal flags are the same as in other giraffes. The back-of ear is a sheeny whitish ( and the tail-tassel is black (

Here is a reminder of what a laryngeal flag looks like, located on the crook of the throat:

There is no laryngeal flag in Giraffa reticulata:

Giraffa reticulata lacks the pale and/or spotless patches on the cheeks that are seen in other giraffes (see

Giraffa reticulata differs from its neighbour, Giraffa tippelskirchi, in having smaller horn-tufts, and this is most noticeable in infants. In the case of the occipital horn-tufts (see, there is virtual absence in Giraffa reticulata. These features have previously been overlooked but are surely taxonomically significant.

Returning to the topic of flags, let us review the colouration of the lower legs.

The fetlocks and pasterns are pale and spotless in all giraffes. However, this does not qualify as conspicuous unless the pale spotlessness:

  • is abruptly defined by relative darkness just above the fetlocks (as in the pedal flag of Giraffa tippelskirchi), or
  • extends to the whole of the lower legs (as in the pedal flag of Giraffa camelopardalis).

By these standards, there is no pedal flag in Giraffa reticulata:

Many photos labelled as reticulata do show lower legs pale enough to qualify as a pedal flag, but these are mainly from the Laikipia region of Kenya ( and from zoos ( and, where there has been hybridisation with Giraffa camelopardalis.

The following unhybridised individual shows the maximum paleness on the feet in the true Giraffa reticulata, which does not qualify as a pedal flag:

The most nebulous and individually variable of the flags is the ilial flag.

Here is a reminder of what an ilial flag looks like, in Giraffa giraffa giraffa: and

There is no ilial flag in Giraffa reticulata:

There is also no pectoral flag in Giraffa reticulata.

Most forms of giraffes show masculine darkening in maturity (see However, I have het to find any photo on the Web that shows this in Giraffa reticulata.

Turning to the head again, the form of the forehead and rostrum is somewhat distinctive in both sexes of Giraffa reticulata.

The bump on the forehead is relatively abrupt. In mature males, the rostrum (anterior to the forehead) tends to remain free of enlargement by ossification:



Compare the latter with mature males of Giraffa tippelskirchi, in which not only the forehead bump but also the rostrum become ossified: The following pair of photos summarises the differences: vs

Another difference between Giraffa reticulata and the hybrid population in the Laikipia region is that, in the latter, some individual mature males develop pallor on the head (e.g.

Having begun this Post with a test, let me end it with another along similar lines. iNaturalists, how would you identify the following?

Posted on November 19, 2021 21:22 by milewski milewski | 1 comment | Leave a comment

November 01, 2021

Just one pangolin remains to emulate the cantilevered bipedal walking of the dinosaurs

Many of the large animals of the Mesozoic ( walked with cantilevered bipedality. Why is it that the only animal locomoting this way today is one species of pangolin?

Our human bias makes it easy to assume that bipedality is, per se, a meaningful category of posture and locomotion. Actually, bipedality is so heterogeneous that using it as an overall description can be misleading (see and and

When the torso is held horizontal, balanced by head and neck on one side and tail on the other, this forms a level beam pivoting on the hind limbs (( Balance is maintained - despite the instability of just two supporting feet - because the mass of the beam anterior to the hips equals that posterior to the hips.

Of course, this needs a sufficiently long and massive tail. However, the potential adaptive advantage is economical walking, because moving one pair of limbs costs less energy than moving two.

Keeping cantilevered balance while running should be relatively easy for the same reason that riding a bicycle hands-off is easier at some speed than slowly. It is the animals able to keep anterior/posterior balance while walking bipedally that are of particular interest.

Cantilevered bipedality is so different from upright (mainly human) bipedality that the two modes have little in common beyond the weight being placed solely on the hind feet.

In Mesozoic times, cantilevered bipedality was pervasive. It evolved independently in at least two major clades of 'dinosaurs' (, the saurischians and the ornithischians, that configured the hips in different ways.

It also occurred over a wide range of families and body sizes, and including flying, feathered forms ( and Even some sauropods (, although walking on all four limbs, probably held the tail horizontal to balance the long neck (

Today, various lizards can run bipedally (, but none walks with cantilevered bipedality.

Birds differ categorically from theropods ( in the bony tail being so short (, with any long caudal feathers so light (, that a cantilever is out of the question.

In this sense birds - despite being the descendants of theropods - are posturally in a category of their own. No bird walks with cantilevered bipedality, the emu (Dromaius novaehollandiae) perhaps coming closest ( because it is odd in depositing fat on its tail.

Various mammals have independently evolved towards emphasis of the hind limbs, but few of them walk bipedally. Some rodents (e.g., lagomorphs and macropodid marsupials hop slowly instead of walking, using gaits unknown in the Mesozoic, or 'walk' by moving first the fore and then the hind feet synchronously ( Few bipedally-inclined mammals other than kangaroos have tails massive enough to act as cantilevers. And kangaroos - far from walking bipedally - cumbersomely use all fours plus the muscular tail as a fifth limb (

Ground sloths ( had a bipedal tendency, but it is unlikely that they walked with cantilevered bipedality. Their tails were muscular enough to act as a prop but not long or massive enough to act as a cantilever (e.g. see The same applies to the extant giant armadillo (Priodontes maximus, and

The only living mammal known to use cantilevered bipedality as its most frequent mode of walking is the second largest-bodied of the eight species of pangolins: the Cape pangolin (Smutsia temminckii, see and and and and second photo in

In all species of pangolins the tails are unusually heavy, partly because they are exceptionally armoured and partly because they are, in arboreal species, exceptionally long (and prehensile). Furthermore, the fore claws of pangolins are so prominent that they tend to obstruct walking on the fore feet. Since all pangolins have particularly economical metabolism and walk slowly, all are candidates for cantilevered bipedality.

However, the small species of pangolins walk on all fours, in some cases placing weight on the knuckles instead of the sole or claws. The smallest species of all (see is so arboreally specialised that it rarely walks on the ground in the first place. The giant pangolin (Smutsia gigantea) is probably capable of bipedal walking but seems usually to use all fours, possibly because its tail has a different proportional size to that of the Cape pangolin, and its fore limbs are particularly muscular.

This leaves - seemingly almost by accident - the Cape pangolin ( as an afterthought of a mode of locomotion which once ruled the terrestrial world.

Posted on November 01, 2021 02:20 by milewski milewski | 7 comments | Leave a comment

November 26, 2021

Explaining the extreme growth-form of Gardenia in the Serengeti

Gardenia volkensii grows as isolated large shrubs - one individual here and another last week - in open savanna in the Serengeti ecosystem. It would hardly be noticed were it not for its extreme sculpting by large mammals: and and and and and and

It is hard to describe this growth-form but 'green coralloid', 'botanical statue' and 'compound bonsai' come to mind. Here we see a combination of gnarled stemwork (e.g. and tight-set foliage, making for a 'caulifoliar' plant.

Various species of woody plants are under pressure by large mouths, and various species of Gardenia occur in various other environments without being sculpted. So what is it about this species, in this ecosystem, that has led to a natural form of topiary?

Here is general information on Gardenia volkensii: and and,KwaZulu%2DNatal%20in%20the%20southeast and and and and

Gardenias are indigenous to Africa, Asia and Australia, and have become horticultural favourites. However, it seems to be only in the Serengeti that this genus is obviously shaped by large mammals.

Here are additional photos of G. volkensii in the Serengeti: and and and and and and and and and and

In trying to understand the niche of any organism, a challenge is to distinguish cause and effect, and to infer the central 'life-history strategy'.

So here are some observations and inferences applying to the genus Gardenia, the species G. volkensii, and the population in the Serengeti.

Gardenias are surprisingly prone to nutrient-deficiencies (as frequently noticed in horticulture, for plants that grow their stems, leaves and fruits slowly even under favourable conditions. Because such supplement-dependent plants would be expected to benefit from the nutrient-recycling by megaherbivores, their presence in the Serengeti ecosystem - albeit in small numbers - is unsurprising.

Instead of defending themselves with spines, gardenias tend to withdraw their foliage and stems. This is seen in extreme form in those species which remain largely underground ( and and and;jsessionid=1AF15650A3AD79CE5529E41C1B07E767?sequence=1 and

Although individual plants maintained in sculpted form are unlikely to produce fruits, it is noteworthy that
G. volkensii is unusual in its genus in being specialised for the sowing of its seeds by 'megafauna'.

Gardenias have technically fleshy (zoochorous) fruits and the seeds are thought to be dispersed by mammals of various body-sizes
(e.g. see and and In the case of G. volkensii, the fruits are particularly large, leathery, long-lasting, and sturdily attached - and thus seemingly attuned to the 'megaherbivory' of the Serengeti.

These greyish fruits, when 'ripe' (and incongruously fragrant), seem designed mainly for the bush elephant (Loxodonta africana) and the eland (Taurotragus oryx). They are difficult to detach from the stems, and too big to fit into the gentle, pursed mouth of the Maasai giraffe (Giraffa tippelskirchi); they are likely to be out of reach of the hook-lipped rhino (Diceros bicornis); and they would probably be cud-chewed to destruction of the seeds by the greater kudu (Strepsiceros zambesiensis), which in any event is absent from this habitat in the Serengeti (see,when%20partially%20decomposed%20by%20fire.).

The bush elephant, when foraging on the foliage, is likely to break branches to some extent despite the flexibility of the wood of gardenias (see and Where free of such damage, the growth-form of G. volkensii is similar to and

The 'juvenile foliage' possessed by saplings of G. volkensii ( is a form of heteroblasty ( shared with various other woody plants. However, this species seems unusual in also possessing a second kind of heteroblasty at a different stage of its life, i.e. diminutive leaves crowded on to nodes, in response to repeated defoliation of old stems.

Thus an explanation may be found in the following combination of factors:

  • a particularly intense regime of pressures exerted by the bush elephant and the Maasai giraffe
  • in open vegetation where the few woody plants tend to be targeted repeatedly
  • partly owing to a bimodal climate (two rainy seasons each year) in which leaves tend to be present on this technically drought-deciduous plant for most of the time.

Because G. volkensii prefers nutrient-enriched soils, its leaves are somewhat attractive to folivores. Because it is 'hardwired' to grow slowly even in response to losses, it has a 'retractive' defence against defoliation; it may capitalise on faeces and urine but it is not stimulated by defoliation to replace its shoots rapidly. And because no member of this genus, as far as I know, has evolved spines, this species has found an unusual way to hug its leaves so close to its stems that plucking them is time-consuming for large mouths.

Based on the above, do readers share with me an impression that the genus Gardenia can be characterised by a combination of three modes: nutrient-inefficiency, slow growth, and spinelessness? And that this generic syndrome is in a way exposed in the sculpting of G. volkensii in the Serengeti ecosystem?

Posted on November 26, 2021 16:35 by milewski milewski | 16 comments | Leave a comment

November 02, 2021

Sonchus oleraceus: undomesticated but perfect for human consumption?

For the last 30 years, Sonchus oleraceus ( has been an important - and perhaps the healthiest - part of my diet.

This herbaceous member of the daisy family is a common weed ( near my home, which has a mediterranean-type climate. The only way I have eaten it is pre-hominid, simply plucking the green leaves ( and chewing them raw on the spot. I do not accept the flowers, even in the form of the buds.

I usually eat about 50 leaves at a time, on average several times per week during the cool and rainy half of the year. That totals about 5,000 leaves per year, with a break in the summer and autumn when S. oleraceus is largely unavailable.

I value salad in my diet, but I have found S. oleraceus so reliable and satisfactory that I have not bought any leafy greens from any sort of shop for the last 15 years. I simply browse when I am out and about, finding my favourite weed easily near sidewalks and in neglected gardens and vacant lots in this metropolitan area.

Herbicides are frequently used to kill weeds here, but it has been easy to find unsprayed plants, and in all these years I have never had the slightest negative reaction from my herbivory.

The leaves are less fibrous than those of dandelion (Taraxacum officinale,, which is scarcer here because of its preference for slightly neglected but frequently watered lawns). However, they are similarly bitterish and moderately astringent. I eat S. oleraceus not for its taste but for its salubrious effects.

It is perhaps ironic that I have never felt drawn to browsing Lactuca serriola ( and, which is also common and weedy hereabouts. Lactuca serriola is, after all, the ancestor of the domestic lettuce (Lactuca sativa, see

The genera Sonchus and Lactuca both have a tendency for the leaves to be somewhat prickly. Sonchus oleraceus can be thought of as a 'relaxed thistle', in which the potentiality for prickliness is seldom realised and the leaves are therefore palatable. Lactuca serriola has a row of prickles on the abaxial side of the mid-rib of the leaf (, which are not thistle-like but are the more discouraging of the two. The prickles, though small, are obvious because the leaves tend to be held by the plant at right angles to the normal orientation. To me, L. serriola looks less appetising than S. oleraceus.

Lettuce has been improved by selective breeding, perhaps to a fault. The cultivated leaves are soft, succulent, virtually free of bitterness, and completely free of astringency. But they also seem hardly worth eating from a nutritional viewpoint.

Sonchus has hardly been subjected to selective breeding ( and, but it presents, in its weedy natural form, something approaching the perfect leafy green from the viewpoint of human health.

At times over the past decades I have grown chicory leaves ( in my garden, as a closely-related but somewhat selectively bred alternative to S. oleraceus. I have also taken trouble to establish another weedy daisy more associated with the tropics, namely Bidens pilosa ( and and, as an annual volunteer in my garden. However, both attempts failed: in the case of Cichorium because the plants require too much care and in the case of B. pilosa because the shoots turn out to be too rich in kidney-irritating oxalates (of which S. oleraceus seems blissfully free).

Sonchus oleraceus remains so underappreciated in human diets that, in my decades of gratefully consuming it and recommending it to others in health-conscious circles, I have never seen it eaten by even one other person.

However, in my personal experience: my everyday environment has presented me with a choice of two species of weedy daisies - one a nominal thistle and the other the prototype for lettuce - originally indigenous to the same parts of Eurasia and gone cosmopolitan in the modern world. And the one that has stood the test of time, prevailing in my diet, is the one that has not been domesticated but could hardly have been improved even if it had.

Posted on November 02, 2021 08:55 by milewski milewski | 8 comments | Leave a comment

November 04, 2021

The mystery of the missing mycorrhizae

Everyone knows that the roots of most plants have an intimate mutualism with fungi, and that the invisible mycorrhizae formed in this way help plants to extract nutrients from soils ( and

However, how many realise that some of these associations are more powerful than others, and that the most powerful mycorrhizae were naturally absent from regions where herbivores are naturally most abundant?

For example, one of the puzzles of global biogeography is that South Africa was virtually devoid of 'supermycorrhizae' common elsewhere in the world.

How did this come about?

Most mycorrhizal fungi have microscopic hyphae. However, ectotrophic mycorrhizae - or ectomycorrhizae for short - can be macroscopic ( and are particularly powerful metabolically. Whereas in other mycorrhizae the fungal cells merely infiltrate the roots, in ectomycorrhizae they form a mycelium actually replacing root tissue. Furthermore, hyphae originating at the roots reach up above the soil surface, breaking down litter such as fallen twigs by oxidising them.

It is from these 'supermycorrhizae' that most wild mushrooms and truffles (both edible and toxic) grow as reproductive structures ( This means that even those naturalists ignorant about microbiology have seen, and may have eaten, ectomycorrhizal fungi ( and and

That ectomycorrhizae are effectively 'supermicorrhizae' is evident in the fact that many of the fastest-growing trees useful to humans, such as pines, oaks, poplars, eucalypts, dipterocarps and casuarinas (, depend on these associations. Most of the timber and paper we use comes from plantations nourished via ectomycorrhizal mutualisms.

Africa includes vast areas of miombo woodland (, dominated by ectomycorrhizal trees ( However, the only species penetrating South Africa are two species of Brachystegia (restricted to a few marginal locations,, one species of Afzelia (sparsely distributed in the north of the country,, and perhaps Manilkara.

Although most of South Africa lies at the same latitudes as lands dominated by ectomycorrhizal trees such as pines, oaks and eucalypts, it naturally lacked ecological counterparts for these trees. Ectomycorrhizae were even absent from South African species of the genera Salix and Myrica, which are ectomycorrhizal elsewhere.

The lack of ectomycorrhizae in South Africa is consistent with the odd treelessness ( and of this country under mediterranean-type and semi-arid climates, where the dominant plants are heath-like shrubs belonging to families (e.g. Asteraceae) and genera (e.g. Erica) unassociated with this type of mutualism.

By contrast, ectomycorrhizae are common in similar climates in Australia (, even where trees are scarce. For example, in mesic heathlands ectomycorrhizal Myrtaceae include small shrubs (e.g. see And in semi-arid scrub some of the acacias in Australia are ectomycorrhizal.

Part of the explanation may be the abundance - even by African standards - of indigenous herbivores in South Africa.

Worldwide, vegetation dominated by ectomycorrhizal plants tends to have sparse populations of herbivores, an obvious example being the boreal forest - where spruces, firs, larches, alders, willows and birches are all ectomycorrhizal.

There is likely to be a fundamental incompatibility between the nutrient-recycling regime associated with faeces and urine, and that associated with fungal decay. The former emphasises bacteria and anaerobic decomposition conserving organic matter in the soil, whereas the latter emphasises macroscopic 'white rot' and aerobic decomposition in which organic matter is wasted.

And a previously overlooked link in any explanation of the biogeographical anomaly is as follows:

South Africa is one of the few lands on Earth where fungus-culturing termites (Isoptera: Termitidae: Macrotermitinae: Odontotermes, and penetrate temperate climates. These insects feed litter, including coarse faeces of herbivores, to underground cultures of the fungus Termitomyces. The fungal culture produces small food-bodies eaten by the termites as well as unusually large mushrooms eaten by humans, and the rapidly recycled nutrients act as fertiliser.

Fungus-culturing termites, by removing surface litter, effectively extend the realm of herbivory at the expense of the sort of decomposition that would favour 'supermycorrhizae'. Whereas ectomycorrhizal fungi promote trees, the fungi mutualistic with macrotermitines are equally powerful in promoting a different form of recycling of nutrients, which favours grasses and herbivores.

In summary:

South Africa was - until the anthropogenic establishment of trees introduced from other continents - unsuitable for ectomycorrhizae. And part of the reason may be that it was the only land on Earth combining temperate climates with a regime of consumption of plant material in which diverse large herbivores, together with various termites operating beyond the usual roles of such insects, precluded the nutritional regime essential to ectomycorrhizae.

Posted on November 04, 2021 11:29 by milewski milewski | 12 comments | Leave a comment

November 06, 2021

Caesalps on southern continents, part 1

Africa, South America and Australia are all southern continents ( and, but they differ biogeographically.

Africa broadly straddles the equator and has always been connected to Eurasia. South America was formerly isolated, but is now connected via North America. Australia remains an isolated southern landmass, an island continent.

Africa has a balance of wet and dry environments, South America has extensive wetness, and Australia has extensive drought (

The comparative biogeography of various families of animals, plants, fungi, and algae on the southern continents is of obvious interest. Here I investigate the caesalps (including both and, a major category of mainly woody and mainly tropical plants capable of dominating vegetation - but with seemingly unpredictable ecological patterns.

I realise that, among the legumes, the pea (Fabaceae) and mimosa (Mimosaceae) families are the clearly-defined ones and 'Caesalpiniaceae' refers to what is really a heterogeneous assemblage of 'other legumes' ( and and However, I think we can learn something interesting about biogeography by categorising the non-pea and non-mimosa legumes as caesalps.

With this caveat in mind, caesalps are surprisingly different in their incidence among our three continents. By incidence I mean the size of the plants and the proportion they occupy in the vegetation.

In a series of four Posts, I will sketch the respective floras of caesalps from this ecological viewpoint. I will then try to explain the overall pattern: major in Africa but minor in Australia, with South America intermediate.

All legumes tend to have nutritional niches in which the supply of the protein-forming element, nitrogen, is supplemented from sources other than the soil. What sets caesalps apart from other legumes is that they are the least likely of the three families to form nodules on their roots, in which bacteria symbiotically fix atmospheric nitrogen.

Of the three southern continents, it is Australia that has the least incidence of caesalps.

About 18 genera are indigenous (, but most of these have failed to penetrate the most extensive vegetation types in Australia, and those that have done so tend to consist of small plants despite the drought-tolerance of trees on this continent ( Furthermore, it is the cosmopolitan genera of caesalps that tend to be prominent in Australia (Senna, Cassia, Chamaecrista, Bauhinia, Caesalpinia).

The few genera of caesalps restricted to Australia (e.g. Petalostylis, Labichea, Barklya and are ecologically unimportant in the sense of being small plants making minor contributions to the vegetation.

Several genera are restricted to tropical rainforest, which covers only a small proportion of this continent. Most of these (e.g. Cynometra, Crudia, Maniltoa, Sindora, Storckiella) occur in tropical Asia and have only marginally penetrated Australia. However, it is noteworthy that Cassia grows to the size of a tree adjacent to rainforest in Australia.

The only genera of caesalps which qualify as dominating any vegetation in Australia are Senna (e.g. and and perhaps Lysiphyllum ( and and However, Senna in Australia forms shrubs rather than trees, and possesses nitrogen-fixing nodules; and plants of Lysiphyllum are small for trees.

The genus Erythrophleum ( and and occurs mainly in Africa, and the genus Peltophorum ( occurs mainly in South America. Both have a minor incidence in tropical Australia.

The only genus recorded to be ectomycorrhizal is Intsia ( and, which has an extremely restricted incidence in rainforest in Australia (

In summary, the incidence of caesalps in Australia is slight in several ways. Those species growing as large plants make only a slight contribution to the canopy where they occur. Most of the tree species have penetrated Australia only slightly. And most of the species deeply penetrating the continent are slight in the sense of being shrubs, dominant over only small areas, and replaced successionally by trees belonging to families other than caesalps.

To be continued...

Posted on November 06, 2021 11:06 by milewski milewski | 16 comments | Leave a comment

November 07, 2021

Caesalps on southern continents, part 2

Having examined caesalps in Australia, let us turn to South America, where tree-dominated vegetation is most extensively rainforest (see but also includes large areas of woodland and savanna.

Caesalps have a far greater incidence In South America than in Australia. However, they are not dominant in the vegetation, with a few exceptions such as Mora ( and Dicymbe (

Shrubby/weedy genera are common, e.g. Caesalpinia, Senna (which includes trees in South America,, Erythrostemon and Chamaecrista.

Many genera form trees, e.g. Libidibia (, Schizolobium (, Copaifera (, Hymenaea (, Eperua ( and Pterogyne ( In the case of several species of Tachigali, the trees can reach up to 40 metres.

Caesalps in the form of trees are present in many vegetation types. However, as in Australia, those types of woodland or savanna that are dominated by legumes tend to favour Mimosaceae (e.g. see

Some examples of genera according to the various ecosystems are as follows:

Ectomycorrizal mutualisms have been recorded in Dicymbe, Eperua and Gleditsia ( and Fixation of nitrogen in nodules has been recorded in Dimorphandra and Tachigali, the latter being remarkable because this nutritional mode is not usually associated with genera capable of growing into such large trees. The following gives further information on the nutritional modes:

To be continued...

Posted on November 07, 2021 06:14 by milewski milewski | 5 comments | Leave a comment

November 08, 2021

Caesalps on southern continents, part 4

In this series of four posts I have summarised the incidence of caesalps according to the size of individual plants and their appropriation of the canopy, averaged over the entirety of each continent.

This crude estimation suffices to show that the southern continents differ by two orders of magnitude in the incidence of legumes other than peas and mimosas: about tenfold greater in South America than in Australia, and about tenfold greater again in Africa than in South America.

This variation is particularly surprising in view of the fact that various genera (e.g. Hymenaea, Cynometra, Copaifera, Erythrophleum, Bauhinia, Piliostigma, Crudia, Senna, Parkinsonia, Dialium) are indigenous to more than one of these continents.

The incidence of ectomycorrhizal ( caesalps varies in the same direction and by similar orders of magnitude, suggesting that the prevalence of caesalps in Africa is linked to a mode of supplementation targeting not only nitrogen but also other nutrient elements.

The intercontinental differences are not merely the result of the drought of Australia and the wetness of South America. Instead, they apply even within categories of climate and arborescence.

Taking tropical savannas for example: in Australia the dominant trees tend to be ectomycorrhizal Myrtaceae (eucalypts), with caesalps relegated to a minor incidence and lacking ectomycorrhizae. By contrast, in Africa the dominant trees tend to be ectomycorrhizal caesalps, of which Brachystegia is representative.

So, if the intercontinental variation ultimately reflects environmental differences, what could these be?

Well, Africa is the continent on which there is the greatest incidence of large herbivores, which has implications for the cycling of crucial nutrients such as phosphorus and zinc ( and

It also differs from South America and Australia in the occurrence of fungus-culturing termites (see, which are the most powerful recyclers of nutrients among the social insects.

Furthermore, the three continents form a series w.r.t. the histories of anthropogenic influence on the cycling of nutrients. The human species has farmed in tropical Africa for most of the last ten thousand years, whereas there was no farming in Australia until Europeans settled. As in various other aspects both ecological and biotic, South America is intermediate.

Miombo woodland and other caesalp-dominated vegetation in Africa has been affected continually by proboscideans. The bush elephant (Loxodonta africana) and other large herbivores were hardly affected by the spate of megafaunal extinctions which wiped out proboscideans from the Americas by ten thousand years ago. Although practised in tropical South America for at least five thousand years, farming seems not to have affected the main types of woodland and savanna (llanos, caatinga, chaco, cerrado), leaving these vegetation types largely unaffected by both shifting cultivation ( and all herbivores heavier than 100 kg.

Because woodlands dominated by ectomycorrhizal caesalps usually occur on relatively nutrient-poor soils, the role of fungus-culturing termites (particularly Macrotermes, may be crucial. These termites concentrate trace elements in their mounds (, which can form patches of sufficient fertility to grow crops. This advantage sets Africa apart from the other two continents and perhaps helps to explain the antiquity and extent of shifting cultivation and the adaptation of caesalps to an anthropogenic regime on a large scale.

Miombo woodland and its equivalent north of the equator are so resilient from slash-and-burn cultivation ( that these vegetation types can be seen as, in some sense, anthropogenic (,agriculture%20practiced%20throughout%20northern%20Zambia.). Disturbance by humans and large herbivores may be integral to the dominance of caesalps.

What looks like pristine woodland may actually be the 'climax' of a successional cycle in which the trees are intermittently broken down by physical means, and their eventual regeneration is facilitated by the patchy suppression of wildfires carried out by farmers and gregarious herbivores.

Posted on November 08, 2021 07:43 by milewski milewski | 2 comments | Leave a comment