Euphorbia prostrata Aiton, prostrate sandmat. Annual, taprooted, several—many–stemmed at base, mat–forming, branches diverging at 20—30°, prostrate, not rooting at nodes, typically < 2 cm tall; monoecious; shoots strongly 2–dimensional (plagiotropic), pubescent; latex white, copious.
Stems cylindric and sometimes with low ridges, < 2.5 mm diameter, flexible, green soon turning pinkish brown except on unexposed surfaces, principal stems not zigzagged, nodes swollen, internodes typically 5—25 mm long but shorter at plant base.
Leaves opposite decussate, simple, short–petiolate, with stipules; stipules 2 (4 per node), attached to node, free on upper side, on lower side pair fused across node, acuminate, < 1 mm long, the upper one > lower one, white to pink, fringed and ciliate on margins; petiole 1—1.5 mm long, curved to orient leaves horizontally; blade broadly ovate or heart–shaped to oblong or roundish, 4—9 × 2.5—6.5 mm, oblique at base, short–serrate and sometimes reddish on margins, obtuse to rounded at tip, inconspicuously pinnately veined with 3 veins at base, pubescent, upper surface gray–green, lower surface lighter in color.
Inflorescence cyathium (= involucre with staminate flowers and 1 pistillate flower), axillary, produced in leafy, cymelike arrays; peduncle < 0.5 mm long; cyathium to 0.7 mm wide (including spreading glands and appendages); involucre inversely conic, < 1 mm long, green, pubescent approaching top, with 5 bracts and 4 glands, the bracts of involucre fused most of length, acute at green tips with whitish margins, the glands alternate with bracts (1 absent), nectar–producing, raised, elliptic to roundish, ± 0.2 mm long, fleshy, reddish, channeled in center, appendaged from just below gland, the appendage petal–like, < gland, whitish to pale pinkish, entire or weakly scalloped on outer margin; staminate flowers 2—4(—5), never in clusters, each with pedicel–like stalk, each flower associated with a bractlet; bractlet threadlike ± 0.5 mm long, white, not fringed, the pedicel short; pistillate flower on a pedicel–like stalk (gynophore), at anthesis gynophore short and erect with only styles exposed, soon after gynophore elongating and becoming recurved with maturing ovary exserted
Staminate flower reduced to 1 stamen; filaments < 0.2 mm; anthers conspicuously dithecal, each sac spheroid, ± 0.2 mm long, reddish, longitudinally dehiscent; pollen yellow.
Pistillate flowerreduced to 1 pistil; ovary superior, 3–lobed broadly ovoid, ± 0.5 mm, light green with or without pink to reddish edges, pilose with most hairs along edges, 3–chambered, each chamber with 1 ovule; styles 3, < 0.3 mm long, 2–branched above midpoint, the branches club– to sausage–shaped, fleshy, pinkish below and ± colorless to transparent pink at tip; stigmas minute.
Fruit capsule, 3–seeded, 3–lobed, broadly triangular–ovoid, 1.5 mm long, pilose, elastically dehiscing along septa and chambers into 6 dry valves (some valve–pairs remaining attached at base) and expelling seeds.
Seed quadrangular–ovoid, 1—1.2 mm long, orangey brown beneath frosty–white epidermis aging grayish green, transversely wrinkled, not noticeably grooved on obtuse, lower ridge.
A. C. Gibson & B. A. Prigge