Scientific name: Rubus occidentalis
Common name: Black Raspberry
(Information for this species page was gathered in part by Sheila Chadman for Biology 220M,
Spring 2001, at Penn State New Kensington)
The American black raspberry is a very abundant component of the Nature Trail's native flora. Black raspberry is found growing densely at any edge or gap in our shaded forest. Raspberry plants can form dense, sometimes impenetrable thickets that function as habitats for many animals, as sheltering enclosures for slow-growing hardwood seedlings that will eventually form the climax sere of our successional sequence, and as seasonally available food for over 150 species of birds and mammals (including hungry hikers!). The American black raspberry is found extensively throughout eastern and central North America. From southern Ontario to Georgia and westward to North Dakota and Oklahoma, this robustly growing plant can come to dominate abandoned fields, stream-sides, construction sites, power line and pipeline right-of-ways, forest edges and tree-fall gaps. In some sections of its range black raspberry grows so rapidly and invasively that it is treated as a weed and a nuisance.
The arcing branches ("canes") of black raspberry grow and mature over a two year time period. The first year's growth (the "primocane") grows quickly and sets a dense mass of leaves. The second year's growth (the "floricane") sets similar leaves but also develops flowers and, therefore, will set fruit. Both types of canes are purple-red in color and are well protected by sharp thorns that arise all along their lengths. The thorns have broad bases and can be either straight or curved. After the second year the floricane dies and turns a dry, grayish-brown. These old canes can accumulate on the ground and also within the standing matrix of the living branches. The living canes are able to generate roots at their growth tips if the cane comes in contact with the soil. This ability to root generates new stock for subsequent branches and further adds to the interwoven complexity of the thicket. Thus, both living and non-living canes and their prodigious thorns contribute significantly to the density and impenetrability of expanding blackberry thicket.
Raspberry leaves are one to four inches long and one to two inches wide. They are oval to lancelate in shape and a dark green on their "upper" surface with a lighter green below. The leaflets are organized into clusters of five around a central petiole. Each leaflet has a double, serrated edge with occasional shallow lobes. The leaf petiole, like the canes, has thorns.
Black raspberry can begin to flower as early as late April and can continue to form flowers through early June. The flowers are small ( three to four millimeters across), white, and found in clusters of three to seven blossoms. The flower stalks (the "pedicels"), like the petioles and the canes, have thorns. Flowers are pollinated by a variety of hymenopterans and dipterans. Black raspberry flowers are able, however, to make berries and seed via self-fertilization and via asexual ("parthenogenetic") reproduction.
The berries are black to purple in color and are between twelve and fifteen millimeters in diameter (size seems to be most dependant upon available moisture). The berries ripen in mid to late June. The aggregate structure of each berry forms from the fusion of the multiple carpals within each flower. Seeds within the berries are dispersed in the feces of the many birds and mammals that consume the sweet, ripened fruit. These dispersed seeds can remain dormant in the soil and litter of an ecosystem for several years until conditions allow germination. Seeds require a winter, cold-stratification before they can germinate and a minimum of at least 128 frost-free days to grow maximally.
Black raspberry plants have a wide tolerance of soil pH and moisture but require a well aerated soil that allows root depths of at least twelve inches. They need full to nearly full sun and can tolerate and rebound from both drought and fire quite well.