Sherardia arvensis L., spurwort, field madder. Annual, taprooted, 1—several–stemmed at base, growing in clumps, decumbent to ± ascending, 10—16 cm tall; shoots with only 1 axillary reproductive shoot per node, ± scabrous and typically short–hispid.
Stems conspicuously 4–sided and strongly 4–ridged, to 1 mm diameter, with ridges descending from leaf midribs, puberulent with stiff, downward–pointing hairs.
Leaves whorled, 4 or 6 per node, simple, sessile to subsessile, stipules 2 indistinguishable from blades in whorl (here treated as leaves); petiole 0—1 mm long, whitish; blade lanceolate to elliptic or oblanceolate, 4.5—10.5(—13) × 1.5—4.5 mm, broadly tapered at base, entire but with stout, upward–pointing hairs on translucent margins, acuminate at tip, pinnately veined typically with only midrib conspicuous and sunken on upper surface and raised with upward–pointing hairs on lower surface, upper surface sparsely short–hirsute.
Inflorescence headlike cyme, axillary, 2—10–flowered within a leafy involucre, bracteate, with some upward–pointing short hairs; peduncle to 20 mm long, stemlike but glabrous and more slender; involucre of 6—8(—10) bractlets subtending pedicels, cup–shaped, bractlets somewhat fused at base, acuminate–lanceolate, 5—9 × 1.2—3.3 mm, mostly green but pale green near the base and with stout short hairs on translucent margins, each bractlet 3–veined, with short–stalked, capitate glandular hairs near pedicel; pedicel < 0.3 mm long, green.
Flower bisexual, radial, 2.5—3 mm across, erect and slightly exserted from involucre; calyx 4—6–lobed, fused to ovary; tube extending slightly beyond the upper rim of ovary; lobes unequal, toothlike, ± 0.5 mm long increasing 2× in fruit, green, short–hispid with colorless, upward–pointing and erect hairs; corolla 4(—5)–lobed, trumpet–shaped (salverform); tube narrow, 2.2—3 mm long, whitish, expanding into funnel–shaped throat 0.5 mm from orifice, mostly lavender; lobes spreading, narrowly ovate, 0.9—1.2(—1.5) mm long, lavender or light to moderate purplish pink; stamens 4(—5), fused to midthroat of corolla, alternate with corolla lobes; filaments 0.5—0.7 mm long, whitish, erect at anthesis then arching out and downward between corolla lobes after pollination; anthers exserted, dorsifixed, dithecal, (0.2—)0.3—0.4 mm long, pink–rose but darker on connective tissue, longitudinally dehiscent; pollen pale pink, apparently shed within flower bud; pistil 1; ovary inferior, deeply 2–lobed, the lobes compressed bell–shaped, 0.5 mm long, enclosed in calyx tube, 2–chambered, each chamber with 1 ovule; style threadlike, 2.7—4 mm long, whitish, unequally 2–branched near tip, the branches 0.25—0.5 mm long; stigmas slightly exserted, capitate, rose–red, papillate.
Fruit schizocarp, 2–chambered forming 2 dry, 1–seeded nutlets (mericarps) with fruit wall ± fused to seed coat; mericarps obovoid, 2.5—4 mm × 1.5 mm, ± cuplike at tip having a persistent, crownlike calyx, (2—)3–ribbed (= veins to calyx lobes) on the convex face and broadly grooved on the lower face, brown, scabrous and short–hispid; calyx lobes on outer 1/2 of rim, erect and webbed between bases.
Seed part of mericarp.
A. C. Gibson & B. A. Prigge