Allegheny Blackberry is a native perennial shrubby plant with stems that are erect to arching, from 2 to 7 feet long with thorns that are large and nearly straight. Arching canes do not usually root at the tips if they touch the ground. Canes live for two years. They are green initially then becoming a dull reddish brown, without any whitish bloom.
The leaves are alternate, 3 - 7 (usually 3 to 5) parted, not lobed but with deep teeth, and on long stalks which have a pair of very short stipules at the base. Upper leaves on the fruiting branches will usually have three leaflets with only the terminal leaflet stalked; larger lower leaves will have 5 leaflets and all can be stalked. The terminal leaflet is always larger. The total leaf is no more than twice as long as wide. The upper surface is medium green, the lower surface much paler due to fine hair. There is glandular hair on the leaf stalks. Fall color can be a brilliant red.
Inflorescence: The flowers and later the fruit are in an open raceme that can have few, or elongate with many, stalked flowers. There is a small green hairy spade shaped bract at the base of each flower stalk. The clusters form on new short side branches that grow from the second year cane. The cluster rises at the end of the new branch or occasionally, springs from the leaf axils. First year canes are vegetative only.
Flowers: The 5-part flowers are large for Rubus, around 1 inch wide with the wrinkly white petals longer than the yellow-green sepals; sepals are triangular and have pointed tips. These reflex when the flower opens. Petals have somewhat rounded tips and narrowed bases. The central section of the flower contains numerous yellow-green carpels, each with a style and these are surrounded by the numerous male stamens that have yellow anthers attached to yellow-green filaments. The anthers turn dark with pollen maturity. The flower stalks have glandular hair as do the stalks of the cluster and the calyx lobes. Altogether - a showy flower.
Fruit: Fertile flowers produce a conic to thimble shaped edible berry composed of many druplets, each containing a single seed. The fruits turn from green to red to purple-black when mature. Fruit forms on second year stems. Picked fruit does not separate easily from the stem. Bloom begins in late May and can continue till July.
Habitat: Allegheny Blackberry grows in rich to poor soils, needing at least partial sun. It will develop good fruit only with lots of sun but does tolerate drier moisture conditions. The root system is a branching taproot and colonies are frequently formed from underground lateral stolons.
Names: The genus name Rubus is the Latin name for bramble and the species name, allegheniensis refers to the Allegheny Mountains. The accepted author of the plant classification, ‘Porter,’ refers to Thomas C. Porter (1822-1901) American botanist and Professor of Botany, plant collector and co-author with John Coulter of Synopsis of the Flora of Colorado. The Common Blackberry has been subdivided by botanists into a number of sub-species most of which are no longer recognized as sub-species but as local variations.
Comparisons: Rubus is complex for identification. These other examples of Rubus that are or have been in the Garden: Wild Red Raspberry, R. idaeus; Thimbleberry, R. parviflorus; Dewberry, R. flagellaris; Black Raspberry, R. occidentalis, and Purple Flowering Raspberry, R. odoratus.
Above: The Blackberry flower is typical of the blackberry/raspberry group with numerous long stamens that have yellow-green filaments and yellow anthers that turn dark at pollen maturity. These surround a cluster of yellow-green carpels with their extended styles. Very showy.
Below: 1st photo - The flowers, leaves and developing fruit - late May. 2nd photo - Thorns are large. The older wood is reddish-brown.
Below: The lower leaves are usually 5-part leaflets on long stalks which can mature to a brilliant red in the fall.
Below: 1st photo - The cluster stalk and flower stalk and the small green bract at the base of the flower stalk are all glandular hairy. 2nd photo - The underside of the leaf is paler in color due to whitish hair. The leaf stalk has glandular hair.
Below: 1st photo - The hairy calyx lobes reflex when the flower opens. 2nd photo - Green fruit developing.
Below: Fruit turns red before maturing to black.
Below: Flowers and forming fruit at the end of May on new side branches of the prior years canes. Note the arching cane and the reddish-brown color of the 2nd year cane.
Notes: Allegheny Blackberry is indigenous to the Garden area. Eloise Butler catalogued it on April 29, 1907. In Minnesota the plant is native to the eastern part of the state, reported in counties along the Mississippi River south of the Metro area and in a large block of counties making up the NE Quadrant of the state except for the Arrowhead. It is quite common in the Garden. It is found in the eastern half North America with populations known in California and British Columbia.
Species: The Minnesota DNR lists 38 species of Rubus in their county location records. The U of M Herbarium makes a list of 54 species that are present or have been reported at one time to be present and gives this disclaimer about the descriptions of the Rubus species: "Rubus is a a very complex taxon with much hybridization, polyploidization, and apomixis occurring within taxa. The group as a whole is difficult to separate into species (especially since both first and second year growth are needed for identification) and there has been much disagreement regarding species distinctions, particularly when statewide or regional populations are considered in the absence of the wider distributions of the species." (Ref. #28C)
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"