Acaciella angustissima (Miller) Britt. & Rose, fern acacia, prairie acacia, white–ball acacia. Perennial herb to subshrub, not spinescent, clonal, rhizomatous from creeping, shallow and horizontal rhizomes, 1–stemmed from each rhizome segment, ascending, to 80 cm tall; shoots with finely compound leaves that are sensitive to touch, short–hairy; rhizomes ca. 3 mm diameter, with ± lobed pith, scales on rhizome ± triangular with blunt tip, 4—5 mm long; adventitious roots from rhizome nodes on lower side.
Stems low–ridged, with 3 ridges descending from leaf, internodes < 10—35 mm long, tough, pilose–hirsute with radiating hairs.
Leaves helically alternate, even–2–pinnately compound with 6—9 pairs of lateral primary leaflets and 15—25 pairs of secondary leaflets, petiolate with pulvinus, with stipules; stipules 2, attached at base of petiole, linear, to 3 mm long, green aging purplish, ciliate on margins; petiole to 25 mm long, pulvinus 1 mm long, shallowly channeled above pulvinus, lacking secretory glands; rachis 2–channeled with central ridge, with pairs of primary leaflets 3—4 mm apart; primary leaflets 6—23 mm long, with pulvinus at base 1 mm long and with an inconspicuous stipel 0.4 mm long on upper side touching top of pulvinus, axis with short hairs; secondary leaflets with petiolule < 0.2 mm long, blades asymmetrically narrowly ovate, < 1.5—2.3 × 0.5—0.8 mm, oblique at base, entire and appressed short–ciliate on margins, obtuse at tip, 1–veined.
Inflorescence headlike raceme, axillary, 12—13 mm across, < 24–flowered, flowers alternate, bracteate; peduncle slender, 15—25 mm long, with pulvinus ca. 1.5 mm long, pilose; bractlet subtending pedicel, < 0.5 mm long; pedicel ± spreading, < 1—2 × 0.25 mm, pale yellow–green.
Flower bisexual, radial, 4.5—5 mm across; calyx 5–lobed, cupped–shaped, ± 0.8 mm long, not appressed to corolla; tube short–hairy to midpoint, alternating green and whitish; lobes broad and rounded, ca. 0.25 × 0.5 mm, membranous with green vein not reaching tip; corolla 5–lobed, obconic; tube cup–shaped, at anthesis to 1 mm long and wide, green; lobes oblong–elliptic, to 1.6 × 0.7 mm, green with narrow white margins, with inconspicuous vein, acute at tip; stamens > 100, free; filaments exserted, slender, threadlike, ± 4 mm long, white; anthers dorsifixed, dithecal, minute, pale yellow, longitudinally dehiscent; pollen pale yellow; pistil 1, exserted, ± 5 mm long; ovary superior, narrowly ellipsoid, 1.5 × 0.4 mm, glossy green, 1–chambered with ca. 10 ovules attached to upper side; style often bent with stigma at or below level of anthers, ca. 3 mm long, white; stigma terminal, minute, glabrous.
Fruit pod (legume), stalked (stipe) at base to 4 mm long, dehiscent, 2–valved, t0 5–seeded, oblong and flat bulging at seeds, 36—50 × 7—10 mm, brown, surfaces veiny, glabrate or pilose, with curved beak at tip; pedicel in fruit ca. 1 mm long.
Seed broadly elliptic to obovate in outline and compressed side–to–side, 4.3—6.2 × 3.4—5.2 × 1.8—3.2 mm, mottled dull brown and light brown, with oblique hilum.
A. C. Gibson