Family Triplostegiaceae

Triplostegiaceae (Hock) Bobrov ex Airy Shaw

~ Dipsacaceae, Valerianaceae

Habit and leaf form. Herbs. Perennial; with a basal aggregation of leaves; rhizomatous, or rhizomatous and tuberous. Leaves opposite; simple. Lamina dissected to entire (dentate to pinnatifid); when dissected, pinnatifid; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins dentate (to pinnatifid).

Stem anatomy. Cortical bundles absent. Medullary bundles absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Vessel end-walls simple.

Reproductive type, pollination. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the abaxial-basal part of the floral tube.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in panicles. The ultimate inflorescence unit cymose. Inflorescences terminal; few flowered, open, terminal thyrses with glandular branches. Flowers (bi-) bracteolate (externally to the epicalyces); fragrant to malodorous (sickly sweet, cf. Valerianaceae); very irregular; zygomorphic. The floral irregularity involving the perianth and involving the androecium. Flowers basically 4 merous; cyclic; tetracyclic. Free hypanthium absent.

Perianth with distinct calyx and corolla (complicated by epicalyces); basically 8; isomerous. Calyx 4; gamosepalous (minute); persistent (the persistent epicalyces becoming indurated). Epicalyx present (this double: an outer one of four conspicuous, basally connate, capitate-glandular, apically uncinate cuspid, persistent bracts, and an urceolate, 8-ribbed, persistent inner one). Corolla 4; deciduous.

Androecial members adnate (to the corolla); free of one another; 1 whorled. Androecium exclusively of fertile stamens (?). Stamens 4; reduced in number relative to the adjacent perianth; oppositisepalous; alternating with the corolla members. Anthers dehiscing via longitudinal slits (these four, separate, rather than two common); tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis degenerating. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer to initially with more than one middle layer; of the ‘dicot’ type. Tapetum amoeboid (the cells multinucleate). Pollen grains aperturate; 3 aperturate; colporate (colporoidate); 3-celled.

Gynoecium 1 carpelled (ostensibly), or 3 carpelled (pseudomonomerous, with only one member fertile). The pistil 1 celled. Gynoecium syncarpous (but pseudomonomerous); eu-syncarpous; inferior. Ovary 1 locular (by abortion of the other two). Gynoecium stylate. Styles 1 (with three xylem strands); apical. Stigmas 1; capitate (small). Placentation apical (?). Ovules in the single cavity 1; pendulous; 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.

Fruit non-fleshy; indehiscent (?); capsular-indehiscent, or achene-like, or a nut (???); 1 seeded (surrounded by the persistent, indurated epicalyces). Seeds endospermic.

Physiology, biochemistry. Iridoids detected; ‘Route I’ type (dimers cf. Dipsacaceae).

Peculiar feature. Epicalyx double, comprising an outer one of four conspicuous, basally connate, capitate-glandular, apically uncinate cuspid, persistent bracts, and an urceolate, 8-ribbed, persistent inner one.

Geography, cytology. Paleotropical. Tropical. Southeast Asia, Eastern Malaysia.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Dipsacales. Cronquist’s Subclass Asteridae; Dipsacales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; campanulid; Order Dipsacales (as a synonym of Valerianaceae).

Species 2. Genera 1; only genus, Triplostegia.

Peng et al. (1995) and Backlund and Nilsson (1997) have provided data on embryology and pollen structure and development of Triplostegia, with cladistic assessments of its taxonomic relationships. The former regarded it as a sister-group to a clade containing Dipsacaceae and Morinaceae, while the latter interpreted it as a subfamily of Valerianaceae.