The families of flowering plants
~ 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. The leaf lamina bifacial, or centric (the palisade tissue reduced). Extra-floral nectaries absent.
Axial (stem, wood) anatomy. Young stems tetragonal. Secretory cavities absent. Cork cambium present; initially superficial. Secondary thickening developing from a conventional cambial ring, or anomalous (?).
The axial 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, phytochemistry. Verbascosides detected. Cornoside detected. Iridoids not 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. Dahlgrens Superorder Lamiiflorae; Scrophulariales (?). Cronquists Subclass Asteridae; Gentianales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order unassigned (? - presumably Solanales or Lamiales).
Species 1 (Polypremum procumbens). Genera 1; Polypremum.
General remarks. 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 (differing in 4 characters from each).
Illustrations. • Polypremum procumbens: Nat. Pflanzenfam. IV (1895).
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 5th March 2018. delta-intkey.com/angio’.