Arenaria benthamii Fenzl, hilly sandwort. Annual, fine–taprooted, 1—several–stemmed at base, divaricately branched in canopy, ascending to spreading, in range to 20 cm tall; shoots with only cauline leaves, somewhat wispy, not glandular–hairy or viscid.
Stems cylindric, slender, ca. 0.5 mm diameter at mid–internode but bulbous just above each node, green, aging ± brittle, internodes to 35 mm long, with 2 vertical lines of puberulent hairs arching downward, the hairs descending from the blade margins.
Leaves opposite decussate, simple, petiolate (lower leaves) and sessile with pair fused across node and sheathing stem, without stipules; petiole indistinct from blade; sheath 0.2—0.4 mm long; blade of lower leaves ovate, of other leaves ascending from fused bases, elliptic or lanceolate to oblanceolate, ascending to spreading from fused bases, in range 4—7.5 × 2—4 mm, tapered at base, entire and sparsely short–ciliate on margins, ± acute at tip, 1–veined sunken on upper surface and raised on lower surface, surfaces without hairs.
Inflorescence dichasial cyme with unequal branches, terminal or axillary, at lower nodes terminal flower diverging at 45° ⊥ plane from 2 branches at fork, cyme several—10+–flowered, bracteate, glabrous; bracts subtending peduncle and each fork 2, leaflike, sessile and fused across node, to 3 mm long decreasing upward, sparsely short–ciliate on margins; pedicel straight, initially short increasing to 25 mm long in fruit, 0.15—0.2 mm diameter, bulbous at base.
Flower bisexual, radial, ca. 3 mm across (calyx); hypanthium inconspicuous; sepals 5, free, overlapping, somewhat unequal, at anthesis acute–ovate, 1.8—2.3 × ± 1 mm increasing 2× and more clearly unequal in fruit, green and white–membranous on margins, 1–veined and outer sepals somewhat keeled, glabrous; petals 5, lacking claw, broadly elliptic, 1.6—1.9 × ca. 0.85 mm, white (veins obscure), obtuse at tip (sometimes with inconspicuous shoulder); stamens 10 in 2 whorls, free, formed on rim of hypanthium; filaments unequal, suberect, 1 mm long (outer stamens) and 0.8 mm long (inner stamens), white, glabrous; anthers dorsifixed, dithecal, 0.2—0.25 mm long, pinkish (outer stamens) and white and often appearing sterile (inner stamens), longitudinally dehiscent; pollen colorless; nectaries projections at bases of outer filaments, green, nectar not observed; pistil 1, very short–stalked (stipe or gynophore); ovary superior, spheroid, 0.7—0.8 mm, light green to midpoint and darker above midpoint with 6 faint lines defining future teeth, glabrous, 1–chambered with 20+ ovules attached to base on a central post on long funiculi; styles 3, spreading, ± 0.7 mm long, translucent–white, stigmatic on inner side of styles and especially on spreading tips, conspicuously papillate.
Fruit capsule, tightly appressed by calyx, consisting petals and stamens, dehiscent at top by 6 terminal teeth scarcely exceeding calyx, in range ca. 20–seeded, before dehiscent ovoid, in range 3—4 × 2mm drying urn–shaped with somewhat recurved teeth, not turning reddish but drying pale brown, smooth teeth acute and ± 0.6 mm long; seeds long–stalked (funiculus) on central postlike placenta; fruit stipe inconspicuous; calyx in range persistent around capsule, lobes somewhat keeled.
Seed sowbuglike to kidney–shaped with strongly curved embryo, in range ca. 0.5 × 0.4 × 0.35 mm, brown and not shiny, cells in longitudinal rows, low–bumpy (tuberculate), each cell wider than long, rounded on back. and lacking papillae.
A. C. Gibson