Parietaria pensylvanica Willd., rock pellitory, cucumber–weed. Annual, taprooted, 1—several–stemmed at base, ascending to erect, in range to 35 cm tall; gynomonoecious; shoots with only cauline leaves, short–hairy and with longer hairs having enlarged bases (pustulate), lacking stinging hairs.
Stems cylindric, to 2.5 mm diameter, pink with rose streaks, short–hairy with mostly arching hairs swollen at base but some pilose hairs.
Leaves helically alternate, simple, petiolate, without stipules; petiole channeled, slender, to 9 × 0.2—0.25 mm, colorless to pale pink with rose veins, slightly constricted near base (abscission zone); blade ovate to lanceolate or elliptic (round), (3—)6—32 × (3—)4.5—13 mm, tapered at base, entire, obtuse to rounded (acute) at tip, pinnately veined with principal veins sunken on upper surface and conspicuously raised and pink to rose on lower surface, sparsely short–hairy with longer hairs on margins, upper surface with minute whitish structures within leaf (cells with cystoliths).
Inflorescence spike, axillary and opposite decussate, of bisexual flowers and pistillate flowers, bracteate; bract subtending spike leaflike, lanceolate, ca. 2 × 0.7 mm;.
Bisexual flower radial, 1 mm across; sepals 4, cupped–ovate, 1 × 0.5—0.6 mm, short–hirsute; petals absent; stamens 4, cupped by sepals with filaments hooked in bud; filaments 1—1.2 mm long, colorless; anthers dorsifixed, dithecal, 0.4 × 0.5 mm, pale green maturing white, longitudinally dehiscent; pollen white; pistil 1; ovary superior, ovoid compressed side–to–side, 0.8 × 0.6 mm, glossy pale green, smooth, with fine, curly hairs surrounding base of ovary, 1–chambered with 1 ovule; stigma exserted, ± sessile, 0.25—0.3 mm across, colorless, papillate and with several spreading short–hirsute hairs at base.
Pistillate flower radial, 1 mm across; calyx 4–lobed; tube wide cylindric, 1.5 × 1 mm, pale green, 9–veined; lobes ovate, ca. 1.4 × 0.6 mm, green above midpoint, 1–veined; petals absent; stamens absent; pistil 1; ovary superior, ovoid compressed side–to–side, 0.8 × 0.6 mm, glossy pale green, smooth, with fine, curly hairs surrounding base of ovary, 1–chambered with 1 ovule; stigma exserted, ± sessile, 0.25—0.3 mm across, colorless, papillate and with several spreading short–hirsute hairs at base.
Fruit achene, ovoid (not compressed), ± 1 × 0.7 mm, glossy white or yellowish; dehiscent within perianth.
A. C. Gibson