This article discusses morphology and identification of the common red and black raspberries in North America: R. idaeus, R. (idaeus) strigosus, R. leucodermis, and R. occidentalis.

Phylogeny preamble

There are many species in the large genus Rubus with the name "raspberry", which generally refers to berries (technically, aggregate fruit) that separate from their receptacle when ripe, giving them a hollowed-out shape (in contrast to blackberries that are not hollow). The commonly cultivated species is Red Raspberry, a familiar sight in supermarkets. Red Raspberries from North America and Europe are often treated as distinct species (R. strigosus and R. idaeus, respectively), but some taxonomies treat them as subspecies (in which case the North American Red Raspberries are R. idaeus strigosus), which is what is currently followed by iNaturalist. Some Red raspberry populations from Asia are also sometimes treated as a separate species, Rubus sachalinensis. The red raspberry lineages are able to interbreed and produce fully fertile hybrids. Plant breeders have worked for centuries to "domesticate" the red raspberry, and many cultivars are now grown commercially in gardens and farms - most of these originate from various crosses between the Eurasian and North American varieties, and many have a bit of ancestry mixed in from other species as well. These hybrid cultivars can frequently be found escaped from cultivation and mingled with the native variety.

Crosses involving red raspberry have also produced other species or commercial crops. Loganberries are a cultivated crop originating from a cross between (European) Red Raspberry and a blackberry (R. ursinus). Similarly, wild Rubus glaucus from the Andes likely originated as a raspberry x blackberry hybrid. Rubus ursinus, a widespread species of western North America, may also be of ancient blackberry x raspberry origin (4).

The closest relatives of the Red Raspberries (apart from their hybrids) are likely the Black Raspberries (4), which consist of at least three widespread species: R. leucodermis in western North America, R. occidentalis in eastern North America, and R. eriocarpus in Central America. Another species, R. nigerrimus, is a rare microspecies restricted to a tiny range in Washington and Oregon that is variably treated as a species or a subspecies of R. leucodermis. R. glaucifolius is another microspecies restricted to a small part of California/Oregon. When present, the colour of the mature berries can easily distinguish red and black Raspberries, but identification is also straightforward with other features when mature berries are absent.

Key field marks to differentiate black and red raspberries

Note: here I am referring to R. occidentalis and R. leucodermis, as "black raspberry" - they are differentiated from red raspberry by the same field marks. They are differentiated from each other by range or by very subtle field marks discussed in their species accounts. I refer to R. idaeus and R. idaeus strigosus as "red raspberry".

When fully ripe berries are present, it can by simple to differentiate the bright red Red Raspberries from the nearly-black purple berries of black raspberries. Unripe berries of black raspberry are red, however, and this frequently leads to them being mistaken for Red Raspberry. Luckily there are some other quick field marks.

The most striking difference is the prickles: black raspberries have strong, curved prickles on their stems. These are shaped like cat's claws and they can hurt or cut if they scratch you. Red Raspberries also have prickles, but these are straight and very thin. As long as you don't grab and squeeze the branches, they won't usually hurt. They are quite weak and are more likely to break than to break your skin (not always...). The best spot to look are the pedicels of the flowers/fruit, where black raspberries have strong prickles, and the common North American variety of Red Raspberry has stipitate glands or very weak straight prickles. European/cultivated varieties of Red Raspberry lack stipitate glands. Cultivated varieties can sometimes have small prickles, but they are not as menacing as black raspberry.

Leaves are also useful: black raspberries usually have only 3 leaflets, and when they have 5 they are arranged palmately, radiating out from a single point. Red raspberries frequently have 5 leaflets, which can be arranged pinnately.

Compare the sharp prickles on the pedicels of black raspberry R. occidentalis (left) to the stipitate glands and weak prickles on red raspberry R. idaeus strigosus (right).

Compare the thick prickles on the 2-year-old (floricane) stems of R. occidentalis (top) to the thin prickles on red raspberry R. idaeus strigosus (bottom)

Compare the palmately arranged leaflets on R. occidentalis (left) to the pinnate arrangement on R. idaeus strigosus (right).

With practice, red and black raspberries can be differentiated at a glance by overall structure. For example, compare these red and black raspberries growing side-by-side: the black raspberries (R. occidentalis, right) have fruit in tighter clusters than the red raspberries (R. idaeus strigosus, left).

Rubus occidentalis

Key field mark: pedicels

The pedicels and peduncles of R. occidentalis are covered by sharp, strong prickles that are curved like cat's claws. Flora of North America suggest that R. leucodermis and R. occidentalis can be differentiated by these prickes: it states that while those on occidentalis are erect, those on R. leucodermis are more often hooked (1).

Flowers

Fruit

The unripe fruits are green.

As they ripen, the fruits begin to turn red, and then become so dark purple that they appear black.

When they are picked or fall off the bush, the fruit (drupelets) easily separate from the torus/receptacle and leave it behind. This gives raspberries their distinctive hollow shape. This distinguishes raspberries with blackberries, in which the fruit is firmly attached to the torus and it stays with the fruit when they are picked (such that the "berries" are not hollow).

Leaves

The leaves of R. occidentalis are deciduous. Each leaf usually has three leaflets (ternate), with a terminal leaflet and a pair of lateral leaflets. The shape of the lateral leaflets is highly variable, even within the same plant. They can be lobed or unlobed, and sometimes divided so deeply that they split in two (pedate), such that the leaf now has 5 leaflets (5-foliate). The apex of the leaflets are described by Flora of North America as acute in R. occidentalis, but acuminate in R. leucodermis, a key ID mark (1) - I believe this is switched around, as the R. occidentalis leaves look quite acuminatae to my eyes!

In these leaves, the lateral leaflets are pedate - they are deeply divided. Some of them are butterfly shaped, and in some of them, they are split so deeply that it looks like they are split into separate leaflets!

The edges of the leaves are toothed or double toothed.

The base of the lateral leaflets holds a key to distinguishing R. occidentalis from R. leucodermis. In R. occidentalis, the leaflets are sessile (that is, they are attached to the stem without a petiolule), while they are described as distinctly stalked in R. leucodermis (1) (but described as subsessile in (3)). With a close view, you can see that the leaf blade of the leaflet starts essentially right where its vein diverges from the pedicel (at least on one side of the vein).

At the base of the leaf, there are a pair of thin (filiform) stipules.

The upperside of the leaves is shiny, without visible hairs.

The underside of the leaves is a pale silvery grey (white-tomentose). The petiolule and larger veins can have small prickles on them. A population of raspberry endemic to a tiny range of Washington/Oregon has leaves that are glabrous, and so the undersides are not silvery. It is not clear whether that population should be considered a subspecies (R. leucodermis nigerrimus) or a separate species (R. nigerrimus) (2)

The leaves near the inflorescence are shaped differently than those on the larger branches. The three leaflets can even be fused into a single leaf.

Stems

Branches in their first year of growth are referred to as primocanes. The primocane stem of R. occidentalis is heavily coated by a waxy substance that gives it a glaucous grey-green colour (pruinose). This is easily rubbed off when touched, revealing a pale green stem beneath. It is armed by strong, decurved prickles that are sparsely distributed. The prickles have a broad base. Thin branches may look pale green with little pruinosity.

Branches in their second year of growth are referred to as floricanes. They are thicker and woodier than primocanes, and brown or purple. They can still be pruinose. Branches sprouting from the floricane bear the flowers and fruits. After the fruiting season, the floricanes die back to make room for the next generation of branches, but the root and crown of the plant are perennial.

Older thickets often have many dried, dead branches from previous seasons. Floricane branches die after they are done fruiting.

Whitebark Raspberry, Rubus leucodermis

Rubus leucodermis is very similar to Rubus occidentalis, but the two species have different ranges: Rubus leucodermis is restricted to western North America and Rubus occidentalis is found farther east.

North American Flora (3) states this:
Rubus occidentalis:

Prickles of the inflorescence scarcely flattened, nearly straight; leaflets dark-green above, abruptly acuminate, with small teeth; stem and branches usually dark bluish-green or purplish, with a bloom.

Prickles of the inflorescence strongly laterally flattened and strongly curved; leaflets yellowish-green above, acute or gradually short-acuminate, with coarse teeth; branches often yellowish.

Flora of North America writes this:
Rubus occidentalis:

Lateral leaflets sessile or subsessile; leaflet apices acute; e North America, Great Plains.

Lateral leaflets stalked (at least 2 larger ones); leaflet apices acuminate; w North America.

Both mention differences in leaf shape (acuminate vs acute), but the first states that Rubus occidentalis is abruptly acuminate vs acute or gradually short-acuminate in Rubus leucodermis, while the second states that it is Rubus leucodermis that is acuminate and Rubus occidentalis acute! The leaves of Rubus occidentalis that I have seen certainly look acuminate to my eyes, while Rubus leucodermis that I have seen appear more acute and less acuminate in comparison - the key might have a typo unless I have been looking at unusual examples. Compare photos above and below. I have also seen prickles on pedicels of presumed Rubus occidentalis that certainly look curved, so that might not be always reliable. Identifying an out-of-range specimen would probably be difficult. Luckily, their ranges do not overlap... as far as we know!

Flowers

Fruit

Unripe fruits start out green and look similar to Rubus occidentalis. Note that the sepals lack stipitate glands: a related raspberry from California, Rubus glaucifolius, has sepals and pedicels covered by stipitate glands.

Leaves

Leaves are very similar to R. occidentalis, but are described as being more acuminate (I think it is the opposite), and the lateral leaflets are on (very short) petioles. These petioles are very difficult to discern from a distant photo, so it is necessary to get a close look.

The shape of the lateral leaflets is variable, they can be deeply lobed and sometimes these lobes split off into separate leaflets (making the leaves pedately 5-foliate). When this happens, the arrangement of the leaflets is palmate (unlike R. idaeus or R. ursinus in which the arrangement is pinnate).

The undersides are silvery, like other raspberries. There are small prickles on the petiole, petiolule, and midvein.

Stems

Stems are similar to R. occidentalis

Red Raspberry, Rubus idaeus

Key field mark: pedicels

The pedicels of the native variety of red raspberry (R. idaeus strigosus) have a dense covering of stipitate glands. They do not have the strong, curved prickles that black raspberries have, but they may have thin, straight, weak prickles.

Flowers

When the flower is flowering, the sepals are strongly curved backwards. After the petals fall off, the sepals slowly unfurl and bend forwards to encase the developing fruit. This photo shows the progression from bottom to top:

Fruit

Fruits of R. idaeuss are the familiar red raspberries that are grown commercially. They are aggregate fruits, which means that each flower has multiple ovaries, each of which can produce a seed. Each fertilized ovary develops into a drupelet, the segments that cluster together to form the raspberry.

Unripe fruits start out green. They are covered by reddish woolly hairs, which appear dense at first, but become sparse as the fruit expands. When very small, the dense hairs make the green fruits look brownish. The fruit is composed of many segments known as drupelets, and each drupelet has the withered remains of the style and stigma of the ovary, which make the berry look hairy.

Once ripe, the berries are bright red and juicy... and tasty!

Like other raspberries, the fruit is only weakly attached to the receptacle, and the receptacle is left behind when the berry is picked. This differentiates raspberries from blackberries, in which the receptacle stays attached to the berry when it is picked.

Leaves

Unlike R. occidentalis, the leaves usually have 5 leaflets. When they have 5 leaflets, they are generally arranged pinnately, while they are palmate in black raspberry (R. occidentalis/leucodermis.

They can also frequently have only three leaflets, like black raspberry, especially on branches that have flowers.

Sometimes the middle two leaflets are fused to the terminal leaflet.

Like R. occidentalis, the leaflets are sessile.

Like Black Raspberry, the underside of the leaves are silvery. They have fine hairs along the veins, and can have small straight prickles (bristles), especially on the main vein.

Like black raspberry, at the base of the leaves are paired stipules that are very thin (filiform)

Stems

Unlike black raspberries, the stems of R. idaeus lack strong, curved prickles. Instead they have thin, weak, straight prickles (bristles). They can have some bluish wax on the stems, similar to black raspberry, but it usually doesn't make the stems as blue as they can get in black raspberry.

Stems that are older than one year (floricanes) become darker purple/brown and woody. The prickles on these stems are still thin and straight, but they can be more painful (not as painful as black raspberry).

Cultivated red raspberry

Most cultivated red raspberries in North America have ancestry from both European (Rubus idaeus idaeus) and North American (Rubus idaeus strigosus) populations (5). Centuries of breeding have resulted in an overwhelming diversity of named cultivars that have been bred for various traits related to taste, ease of harvest and storage, yield, disease resistance, fruiting time, climate adaptation, and more (5). Plant breeders have also used hybridization to incorporate genetic material from various other species of Rubus into red raspberry cultivars: for example, 'Autumn Bliss' raspberries include influences from Rubus arcticus (5), which is not particularly closely related to raspberries (4). Many modern cultivars have a small amount of ancestry from black raspberry in order to improve the firmness of the berries.

Each domestic cultivar can vary in its appearance, and different cultivars may rise or fall in popularity or be popular in different regions. For example, garden centres near me in Toronto sell 'Heritage', 'Bushel & Berry Raspberry Shortcake', 'Boyne', 'Coho', and 'Meeker' raspberries, but garden centres in colder, hotter, wetter, or drier climates may carry different cultivars. Despite their variation, cultivated raspberries can usually be distinguished from wild Rubus idaeus strigosus by differences in their prickles and glands, especially on the pedicels. While wild red raspberries usually have pedicels with many stipitate glands and a few thin straight bristles, domesticated raspberries can have entirely bare pedicels (lacking stipitate glands), or can have strong curved prickles (resembling Rubus occidentalis but not as menacing). The stems can be entirely smooth and lack prickles, or can have thick triangular prickles (vs. the dense thin bristles of Rubus idaeus strigosus)

Pedicels

This cultivar has thin curved prickles on the pedicels. Note the lack of stipitate glands.

Flowers

Flowers generally look the same as wild red raspberry, except for the lack of stipitate glands on the sepals. Some cultivars have been bred to produce flowers on the first-year (primocane) branches, rather than only on the older second-year (floricane) branches.

Leaves

The leaves are generally similar to wild red raspberry, with 3-5 leaflets and pinnate arrangement. I have seen some with very large leaves.

Leaf undersides:

Look how large these leaves are compared to my hand!

Stems

Some cultivars have robust triangular prickles. They are much stouter than Rubus idaeus strigosus prickles, but not as strong and curved as Rubus occidentalis, and they are red.

This mature bush had stout prickles on the lowest parts of the primocanes, but the rest of the stems lacked prickles entirely and was smooth to touch, with only a few scattered nearly-flat prickles.

This 2-year-old floricane has peeling brown bark and no prickles.

Glossary

Floricane: in gebus Rubus, a branch (cane) that is in its second year of growth, and which can bear the inflorescences (fruits/flowers)
Pedicel: the stalk of an individual flower
Peduncle: the stalk of multiple flowers/fruit (their pedicels attach to the peduncle)
Primocane: in genus Rubus, a branch (cane) that is in its first year of growth
Stipitate gland: glands that are elevated on a thin stalk (stipe)
Ternate: of a leaf, compound with three leaflets

Select References

(1) Flora of North America Vol 9. Rubus leucodermis. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250100437
(2) Flora of North America Vol 9. Rubus leucodermis var. nigerrimus. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250100726
(3) Small, John Kunkel. 1905. North American Flora, Volume 22. pg 443-444. https://books.google.ca/books?id=RBolAQAAMAAJ&pg=PA444&lpg=PA444
(4) Carter KA, Liston A, Bassil NV, Alice LA, Bushakra JM, Sutherland BL, Mockler TC, Bryant DW and Hummer KE (2019) Target Capture Sequencing Unravels Rubus Evolution. Front. Plant Sci. 10:1615. doi: 10.3389/fpls.2019.01615
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Posted on 04 July, 2022 22:12 by elsemikkelsen