Family Theligonaceae

Theligonaceae Dum.

Alternatively Thelygonaceae auctt., Cynocrambaceae Nees~ Rubiaceae: Wunderlich 1971

Habit and leaf form. Herbs (with more chloroplasts in the pith of the stem than in the cortex). Plants somewhat succulent. Annual, or perennial; with neither basal nor terminal aggregations of leaves. Leaves opposite (below), or alternate (sometimes, above, by suppression of one member of each pair); fleshy; petiolate; simple. Lamina entire; pinnately veined, or palmately veined. Leaves stipulate. Stipules interpetiolar; with colleters (on the inside, near the tip). Lamina margins entire.

Leaf anatomy. Stomata present; paracytic.

Lamina dorsiventral. The mesophyll containing calcium oxalate crystals. The mesophyll crystals raphides (in idioblasts).

Stem anatomy. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with fibre tracheids, or without fibre tracheids (female flowers). Sieve-tube plastids S-type.

Reproductive type, pollination. Plants monoecious. Gynoecium of male flowers absent. Pollination anemophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary and aggregated in ‘inflorescences’ (the males mostly borne singly or paired opposite the leaves at the upper nodes, unless each ostensible ‘flower’ is interpreted as a cluster; the females mostly in simple axillary dichasia at the lower nodes). The ultimate inflorescence unit cymose. Inflorescences axillary; mostly in 1–3 flowered cymes — assuming that what are ostensibly male flowers are not interpreted as inflorescences. Free hypanthium absent. Hypogynous disk absent.

Perianth ostensibly sepaline (in male flowers, where it is closed in bud, subsequently becoming valvately 2–5 partite with broad, revolute segments; unless the ‘perianth’ is here interpreted as an involucre surrounding a reduced flower cluster), or petaline (the female flowers with a membranous, oblique, tubular, 2–4 valvately toothed perianth, interpreted as a corolla); 2–5. Calyx of the male flowers, if so iterpreted, 2–5 (partite); valvate. Corolla of female flowers, if so interpreted, 2–4 (toothed); gamopetalous; valvate; vase-shaped (produced above into a narrow tube); unequal but not bilabiate.

Androecium in male flowers, (2–)7–12(–30). Androecial members branched (i.e. perhaps thus interpretable), or unbranched; free of the perianth; free of one another, or coherent; sometimes 2–5 adelphous (the stamens sometimes in groups of 2, 4 or 6). Androecium exclusively of fertile stamens. Stamens (2–)7–12(–30); erect in bud (the anthers becoming pendulous at anthesis); filantherous (the filaments filiform). Anthers versatile; dehiscing via longitudinal slits; bilocular; tetrasporangiate. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Pollen grains aperturate; 4–8 aperturate; (brevi-) colpate to porate; 3-celled.

Gynoecium ostensibly 1 carpelled. The pistil 1 celled. Gynoecium ostensibly monomerous (but ‘really’ pseudomonomerous?); ostensibly of one carpel; superior. Carpel stylate; with a gynobasic style (this filiform, exserted from the mouth of the perianth); 1 ovuled. Placentation basal. Ovules non-arillate; campylotropous, or amphitropous; unitegmic (the integument massive); tenuinucellate (Wunderlich 1971). Endothelium not differentiated. Embryo-sac development Polygonum-type. Antipodal cells formed; 3; not proliferating; ephemeral. Endosperm formation nuclear. Embryogeny probably solanad.

Fruit non-fleshy. The fruiting carpel indehiscent; nucular, or drupaceous. Fruit 1 seeded (the seed hippocrepiform). Seeds endospermic. Endosperm oily. Cotyledons 2. Embryo strongly curved.

Seedling. Germination phanerocotylar.

Physiology, biochemistry. Iridoids detected; ‘Route I’ type (normal). Verbascosides not detected. Betalains absent.

Geography, cytology. Holarctic. Temperate to sub-tropical. Canaries, Mediterranean, Southwest China, Japan. N = 10 or 11.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Gentianiflorae; Gentianales. Cronquist’s Subclass Asteridae; Rubiales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Gentianales (as a synonym of Rubiaceae).

Species 3. Genera 1; only genus, Theligonum.

Wunderlich 1971.

Illustrations.
• Technical details (Theligonum).