Prunus rivularis Scheele, thicket plum, creek plum. Thicket–forming shrub, cloning via shallow, horizontal roots, shoots from spreading roots erect, 200—400 cm tall, in range dense clones to 30 m long; shoots often 2–dimensional (plagiotropic), not spinescent.

Stems

Stems somewhat angled, with 3 ridges descending from leaf, zigzagged, internodes to 20 mm long; bark on small branches satiny reddish brown having horizontal lenticels, with scattered stiff short hairs

Leaves

Leaves helically alternate, simple, petiolate, with stipules; stipules 2, attached to petiole at top of wing, acuminate, to 7 × < 1 mm, with 1—2 basal lobes or without lobes, having 1—several, fleshy glandular teeth on margins; petiole to 20 mm long, winglike to 3 mm below stipules, above wings strongly channeled, having 1—several glandular teeth along ridges above midpoint, channel stiff–hairy; blade ovate–lanceolate, (15—)50—95+ × (9—)22—35+ mm, tapered at base, low–serrate initially with glandular tips on teeth base–to–tip on margins, acuminate to acute at tip, pinnately veined with principal vein slightly sunken on upper surface and raised on lower surface, often with a pair of glands at base of blade, glands on teeth abscising as blade growing, short–villous aging glabrescent or hairs mostly present along veins on lower surface.

Inflorescence

Inflorescence 2—4–flowered cymelike clusters, on lateral shoots < 50 cm long on stubby shoots to 3 mm long, flower–bearing spur shoots covered with bud and bract scars, bracteate; bractlet subtending pedicel fan–shaped, to 3 mm long, early–deciduous; pedicel at anthesis 8—10 mm long not increasing in fruit, glabrous.

Flower

Flower bisexual, radial, 12—14 mm across; pleasantly fragrant; hypanthium cup–shaped, ca. 2.5 × 1.7 mm, green, 10–veined with ± raised veins on outer surface; sepals 5, widely spreading, narrowly ovate cupped upward, spreading later somewhat reflexed, spatulate, 2.5—3 mm long, green but having white margins below midpoint, with minute red glandular teeth and fringed at least above midpoint, upper surface soft–hairy, lower (outer) surface glabrate and wrinkled; petals 5, spreading, obovate and somewhat cupped, 5—7 mm long, white, short base (claw) short glandular–hairy, on upper surface sometimes with minute teeth above midpoint, abscising with scar between sepals; stamens ± 30 in several whorls, free arising from rim of hypanthium; filaments slender, 5—6.5 mm long, white, never straight, glabrous; anthers dorsifixed, dithecal, 0.4—0.45 mm long, light yellow, longitudinally dehiscent; pollen green–yellow; pistil 1, 10—11 mm long; ovary superior, narrowly ovoid–ellipsoid, 1.5 mm long, green, glabrous, 1–chambered with 2 ovules; style cylindric, light green; stigma capitate, hemispheric, dark green.

Fruit

Fruit drupe, with 1 stone, spheroid, 12—20 × 12—20 mm, red and somewhat glaucous, pulp juicy, 3—4 mm thick, orangish, very tart; stone (endocarp) almond–shaped, 10—14 × 8—9 × 5—5.5 mm, extremely hard.

A. C. Gibson