Family Polypremaceae

Polypremaceae L. Watson ex Doweld & Reveal

~ Loganiaceae sensu lato, Tetrachondraceae

Habit and leaf form. Diffuse, procumbent herbs (with more or less dichasial branching). Annual, or perennial. Leaves opposite; sessile; connate; simple. Lamina entire; linear. Leaves stipulate, or exstipulate (?). Stipules if present, interpetiolar (?). Lamina margins entire.

Leaf anatomy. Extra-floral nectaries absent.

Lamina isobilateral, or centric (the palisade tissue reduced).

Stem anatomy. Young stems tetragonal. Secretory cavities absent. Cork cambium present; initially superficial. Secondary thickening developing from a conventional cambial ring, or anomalous (?). Xylem with fibre tracheids.

Reproductive type, pollination. Plants hermaphrodite; homostylous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary; axillary (to the opposite leaves); (bi-) bracteolate (the bracteoles sepal-like); small; regular; 4 merous; tetracyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 8 (usually), or 10; 2 whorled. Calyx 4 (usually), or 5; 1 whorled; gamosepalous; toothed (the segments rigidly linear from broad bases). Calyx lobes markedly longer than the tube. Calyx regular. Corolla 4 (usually), or 5 (slightly shorter than to slightly longer than the calyx); 1 whorled; gamopetalous (hairy in the throat). Corolla lobes markedly shorter than the tube (the tube 1.5 to 2 times as long). Corolla imbricate (the lobes blunt); campanulate and tubular; regular; white.

Androecium 4 (usually), or 5. Androecial members adnate (inserted somewhat above the middle of the corolla tube); free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 4 (usually), or 5; isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous (the filaments short). Anthers dehiscing via longitudinal slits; introrse. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; more or less eu-syncarpous; partly inferior (according to Adams (1972), and ’almost completely superior‘ according to Leeuwenberg and Leenhouts (1980)). Ovary 2 locular. Gynoecium stylate. Styles 1; apical. Stigmas 1; 1–2 lobed; capitate. Placentation basal to axile (the placentas not bilobed, oblong, adnate to the base of the septum). Ovules differentiated; 20–50 per locule (‘many’); anatropous; unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Hypostase absent. Endosperm formation cellular. Endosperm haustoria present; chalazal, or micropylar. Embryogeny onagrad.

Fruit non-fleshy; dehiscent; a capsule (somewhat compressed at right angles to the septum). Capsules loculicidal and valvular. Fruit 20–100 seeded (to ‘many’). Seeds endospermic; small; wingless (and not flattened). Embryo well differentiated. Cotyledons 2. Embryo straight.

Physiology, biochemistry. Iridoids not detected. Verbascosides detected. Cornoside detected.

Geography, cytology. Holarctic and Neotropical. North and Central America, Colombia, West Indies. 2n = 22. Supposed basic chromosome number of family: 11. Ploidy levels recorded: 2.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Scrophulariales (?). Cronquist’s Subclass Asteridae; Gentianales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order unassigned to Order (? - presumably Solanales or Lamiales).

Species 1. Genera 1; Polypremum.

This genus was evidently misplaced in the traditional Loganiaceae sensu lato, and does not even seem to belong in the Gentianales. Its affinities are usually assumed to lie with Scrophulariales (cf. Struwe et al., 1994), but analyses of the descriptions compiled here place it equally close to Scrophulariaceae and Solanaceae (4 differences from each).