Family Boraginaceae (sometimes separated in Ehretiaceae).
Habit and leaf form. Prostrate herbs. Annual. Mesophytic. Leaves small; alternate; spiral; petiolate; non-sheathing; simple. Leaf blades entire; conspicuously asymmetric; obovate; pinnately veined; cross-venulate. Mature leaf blades adaxially pubescent; abaxially pubescent. Leaves without stipules. Leaf blade margins crenate. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers solitary; extra- axillary; subsessile; inconspicuously bracteate, or ebracteate; minute to small; regular; 4 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 8; 2 -whorled; isomerous. Calyx present; 4; 1 -whorled; gamosepalous; lobed; lobulate, or blunt-lobed, or toothed; campanulate, or tubular; unequal but not bilabiate; persistent; non-accrescent. Calyx lobes ovate. Corolla present; 4; 1 -whorled; gamopetalous; lobed; toothed; imbricate, or valvate; obcampanulate; regular; glabrous abaxially; glabrous adaxially; white to cream. Androecial members definite in number. Androecium 5. Androecial sequence not determinable. Androecial members adnate (epipetalous); all equal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 5; remaining included; oppositisepalous; all alternating with the corolla members. Filaments glabrous. Anthers dehiscing via longitudinal slits; introrse; tetrasporangiate; unappendaged. Gynoecium 2 carpelled. The pistil 4 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary plurilocular (4-lobed); 4 locular (the ‘true’ locules with incomplete false septa). Locules partially secondarily divided by ‘false septa’. Gynoecium median; stylate. Styles 1, or 4 (-branched); partially joined; 4-branched (by dividing twice); apical. Stigmas 4 (1 on each style branch); 2–4 - lobed. Placentation axile to basal. Ovules 2 per locule; pendulous (rarely), or ascending; non-arillate; hemianatropous.
Fruit and seed features. Fruit fleshy; a schizocarp. Mericarps 4; comprising nutlets. Fruit 4 seeded. Seeds endospermic, or non-endospermic.
Etymology. After Cadwallader Colden (1688–1776), Scottish physician, surveyor-general of New York and later lieutenant-governor; collected American plants for Linnaeus.