Limnosciadium pumilum (Engelm. & A. Gray) Mathias & Const., prairie dogshade. Annual, with clustered fibrous roots at base of shoot (inconspicuously taprooted), not rosetted, several–stemmed at base, repeatedly forked by forming an inflorescence and an ascending branch from node of successive cauline leaves, in range < 20 cm tall; shoots with basal leaves and several cauline leaves, foliage axes and lobes mostly slender to threadlike, all aboveground plant parts totally lacking hairs, when crushed with a faint celerylike (Apium) smell (not strongly aromatic); adventitious roots arising from several basal nodes, the buried stem to 4 mm diameter, pinkish rose, and having broad ridges and deep furrows, the largest adventitious roots more dominant than the initial taproot (“fascicled”).
Stems ridged with 1—2 broad furrows along each internode, on ascending shoots to 2.5 mm diameter, with 3 ridges descending from each leaf, tough, internodes to 65 mm long, green having colorless ridge edges often with beadlike cells.
Leaves helically alternate, to 85 mm long, unlobed or unpredictably with 1 or more lateral lobes oddly arising from the channel on the upper side of leaf axis, petiolate with base sheathing almost 360° and not inflated, with stipules; stipules 2, = membranous wings attached to base of petiole including sheathing stem, 3—5 × 0.4—0.9 mm, margins somewhat crisped; petiole flat to shallowly channeled on upper side above stipules and with several ridges on other sides, to 20 mm long, indistinct from blade, green with minute, beadlike cells along colorless edges; blade and lobes mostly linear, on robust leaf terminal lobe narrowly elliptic to 8 mm wide, lobes entire, mostly 1–veined.
Inflorescence compound umbel, lateral opposite leaf at node and paired with continuing shoot, with slender axes, flat–topped, to 40 mm across, of (2—)4—8 clustered umbellets, many–flowered, umbellet 6.5—13 mm across, of 7—11 bisexual flowers, bracteate, glabrous; peduncle slender, ridged and 5–sided, (< 1 and subsessile) 15—40 × 1 mm; involucre of bracts subtending primary rays, spreading, free at base, acute and oblong or linear to triangular, 2—4 × 0.25—0.8 mm, 1–veined, green but the largest with colorless margins, persistent; primary rays to 8, unequal, slender, strongly 5–ridged, 4—16.5 mm long increasing somewhat in fruit, green; bractlets of involucel subtending outer pedicels 5—6, partially fused only at base, triangular to ovate, 1.3—2.5 × 0.15—0.65 mm, green with narrow colorless margins; pedicels unequal, cylindric, at anthesis (1—)2—5 mm long, with some beadlike cells.
Flower bisexual, radial, ± 3.5 mm across; sepals 5, fused only at base (< 0.35 mm), unequal, 0.8—1 mm long, ascending, triangular, 0.35—0.8 mm on each flower and increasing in fruit, fleshy, green with narrow white margins and sometimes reddish at tip, persistent; petals 5, widely spreading, equal, roundish, 0.9—1.3 mm, white, with low midridge on upper surface but lacking tail–like tip (blunt–acute at tip); stamens 5, free; filaments initially ascending aging widely spreading, ± 1 mm long, white; anthers dorsifixed, dithecal, 0.4—0.45 mm long, rose aging darker, longitudinally dehiscent; pollen white; pistil 1; ovary inferior, inconspicuous beneath calyx, 0.3—0.5 mm long, glossy green, not obviously 2–lobed, glabrous and lacking projections or ribs, 2–chambered, each chamber with 1 ovule; styles 2, ascending, with a nectar–producing platform (stylopodium) on top, D–shaped halves of stylopodium together 1 mm across and 10–lobed with scalloped margin, ivory–colored, initially flat becoming domed in fruit, moist with nectar; styles 2, at anthesis scarcely visible above stylopodium projecting < 0.15 mm, colorless, in developing fruit 1 mm long and white; stigmas terminal, minute.
Fruit schizocarp, of 2 dry, 1–seeded halves (mericarps), before splitting subspheroid to barrel–shaped and not obviously 2–lobed, in range 2.7—3.1 × 2.3—2.5 mm + conic stylar structure at top and ascending lobes of calyx, before drying mericarp wall glossy with fine stripes and smooth, 2 lateral ribs (decurrent from paired sepals) much broader and maturing corky; sepals ascending, triangular, 0.6—1.1+ mm long; stylopodium on top erect wavy and stigmatic lobes persistent.
A. C. Gibson