Yucca arkansana Trelease, arkansas yucca, soapweed. Perennial herb, clonal (limited), evergreen, usually not spinescent, with caudex, rhizomatous, fibrous–rooted, ± hemispheric–rosetted, usually 1–stemmed at base, in range with inflorescence to 110 cm tall; shoot with flexible 30+ basal leaves and cauline leaves (during spring growth upper internodes between basal leaves eventually elongating to become the lower portion of an inflorescence), glabrate; rhizome ± upright and lobed, ca. 7 mm diameter, white later forming peridermlike cover; fibrous roots along upright portion of rhizome. Stem (peduncle): hidden by rosette of basal leaves, 6—12 mm diameter, lower portion with no visible internodes.
Leaves helically alternate, simple and sessile, without stipules; blade ascending, strap–shaped, in range < 230—500 × (6—)9—13 mm, the widest near midblade and gradually tapered to tip, tough, dull green, flaring at base, entire and initially with short hairs, aging with margin separating as slender fibers < 50 mm long (filiferous) grayish and peeling, prow–shaped at tip, parallel–veined converging at tip but veins not conspicuously raised, upper surface shallowly concave, lower surface convex and sparsely short–hairy.
Inflorescence in range raceme, to 50–flowered, flowers pendent, bracteate, glabrous; peduncle (stem) ± cylindric, in range to 11 mm diameter above basal leaves, solid and fibrous aging woodlike; bracts along peduncle (cauline leaves) to midpoint, leaflike, to 97 mm long decreasing upward, sheathing at base, entire, long–tapered to fine tip, each with axillary bud; rachis ridged, each ridge descending from bract; bract and bractlet subtending pedicel triangular, the outer 11—13(—38) × 6 mm, > pedicel, with many parallel veins, with persistent thickened base and aging scarious, the bractlet acuminate–triangular, mostly 8—9 × 3 mm, at anthesis > pedicel, < bract and oriented 90° from bract, scarious; pedicel cylindric, to 7 mm long, yellow–green, with constriction for abscission at top.
Flower bisexual, radial, ca. 30 mm across; tepals 6 in 2 whorls, ± monomorphic, white with parallel green veins, of outer whorl obovate, in range 34—35 × 16—18 mm, midrib approaching tip forming crest of vesicular cells, somewhat prow–shaped at tip having colorless, club–shaped hairs; of inner whorl ovate, 34—37 × 18—22 mm, slightly wider than outer tepals; stamens 6 in 1 whorl, free; filaments appressed to ovary, narrowly club–shaped, at anthesis 14—17 × 3—3.7 mm (1.5—1.8 mm wide at base), white at base to greenish white approaching slender top, conspicuously papillate; anthers dorsifixed–versatile, dithecal, arrow–shaped, 3.6—4 mm long, ivory–colored, longitudinally dehiscent; pollen white; pistil 1, ± same height as stamens; ovary superior, low 6–lobed, ± 15 × 6 mm, cream–colored, glabrous, 3–chambered, each chamber with 2 stacks of many ovules; style 3–lobed, 4 mm long, with constriction below lobes, the stigmatic portion 3–sided, with fleshy lobes 2 × 2.6—2.8 mm and channeled but not to tip.
Fruit capsule, septicidal, 3–valved, splitting from tip downward < 20 mm thereby spreading to reveal 6 stacks of seeds (sometimes most aborted or damaged by predator), erect, when still green 36—58 mm long, length ± = width with short point (style), hard, plump, dark gray or charcoal brown aging dark gray, valves conspicuously veined with cross, parallel fibers; pedicel in fruit < 30 mm long.
Seed ± D–shaped in outline and strongly flattened, 9—11 × 8—10 mm, black.
A. C. Gibson