Rubus ursinus

California blackberry

Rosaceae

The Basics

Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (flowering plants). Class - Magnoliopsida (dicotyledons). Subclass - Rosidae. Order - Rosales. Family - Rosaceae (rose family). Genus - Rubus L. (blackberry). Species - Rubus ursinus Cham. & Schltdl. (california blackberry).

Ecology: California blackberry is a low-growing, California or climbing, native evergreen shrub. This mound-building shrub can grow to 5-6 m in length. The densely prickled stems are greenish when young but turn brown at maturity. The somewhat prickly, deeply-lobed, alternate leaves are palmate and a lighter green color beneath.

The stems of most blackberries are biennial. Sterile first-year stems, known as primocanes, develop from buds at or below the ground surface and produce only leaves. Lateral branches, or floricanes, develop in the axils of the primocanes during the second year and bear both leaves and flowers. Perfect flowers of California blackberry develop in clusters of 2 to 15 near the ends of leafy branches. Fruit is red and hard when immature but shiny black when ripe. Fruit is oblong or conical, somewhat bristly, and up to 2 cm in length. Aggregates of druplets, commonly referred to as "berries," are sweet and flavorful at maturity.

Identification

A mounding shrub or vine with bristly, running stems; large, trifoliate leaves; and clusters of white flowers near the tips of lateral shoots. The flowers differ from those of other blackberries because of their widely spaced, narrow petals. Flowers are followed by edible, black berries. Ranges from 2-5 ft. high and more than 6 ft. wide.

Threats

Fire effects: California blackberry is described as "rather tolerant" of fire. Although it may be top-killed, underground regenerative portions of this shrub generally survive. Fires of relatively high severity or intensity, with the potential to harm belowground regenerative structures, appear to be the most damaging to California blackberry. Most California blackberry seed stored on-site in the soil or duff is probably unharmed by fire.

California blackberry is capable of vegetative regeneration following fire through nonrhizomatous basal sprouts or root "suckers". Basal sprouting is believed to be of primary importance, and often results in a large number of sprouts. This low-growing shrub can also root at the stem nodes and can presumably spread quickly where portions of the aboveground stem remain undamaged. Vegetative spread is generally both vigorous and rapid.

Seedbanking is also an important postfire regenerative strategy. Seeds accumulate in the soil or duff, remaining viable long after this seral species has been eliminated from mature forest communities. Seeds commonly germinate in great abundance after fire.

Reproduction

California blackberry exhibits vigorous vegetative regeneration but also commonly reproduces through seed. Reproductive versatility is common in the Rubus genus, with sexual reproduction, parthenogenesis (development of the egg without fertilization), pseudogamy (a form of apomixis in which pollination is required), and parthenocarpy (production of fruits without fertilization) occurring widely.

Seed production - Most blackberries produce good seed crops nearly every year. During the first year of development, blackberries grow from perennial rootstocks or creeping stems and produce sterile vegetative shoots known as primocanes. Lateral branches which produce both leaves and flowers (floricanes) develop in the axils during the second year. Black shiny drupelets are produced on the floricanes of California blackberry.

Germination - Blackberry seeds have a hard, impermeable coat and dormant embryo; consequently, germination is often slow. Most blackberries require, as a minimum, warm stratification at 30 to 20 degrees C for 90 days, followed by cold stratification at 2 to 5 degrees C for an additional 90 days. These conditions are frequently encountered naturally as seeds mature in summer and remain in the soil throughout the cold winter months.

Seedbanking - The seeds of most blackberries remain viable for at least several years after being buried in the soil or duff.

Vegetative regeneration - Most species within the Rubus genus are capable of vigorous sprouting from root or stem suckers, or rooting stem tips. California blackberry sprouts readily from "suckers" (presumably root suckers), or "nonrhizomatous sprouts" after fire or mechanical disturbance. It is also capable of spreading rapidly from trailing stems which root at the nodes. These modes of vegetative spread occur even in the absence of disturbance.

Species Distribution

Citation

USDA Plant Database
USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov, 4 February 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Flora of North America
Flora of North America Editorial Committee, eds.  1993+.  Flora of North America North of Mexico.  19+ vols.  New York and Oxford.

Intermountain Herbarium
Consortium of Intermountain Herbaria. 2016. http//:intermountainbiota.org/portal/index.php. Accessed on February 04.

Burke Museum Plant Image Collection
The plant image collection at the Burke Museum, University of Washington.

Jepson Manual
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA. $131.95, hardcover; 1600 pages. ISBN-13: 978-0520253124.