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The families of flowering plants

L. Watson and M.J. Dallwitz

Retziaceae Bartl.

~ Loganiaceae, Stilbaceae.

Habit and leaf form. Simple or sparingly branched, ericoid shrubs (the erect or closely ascending, stout stems clustered on a large, persistent lignotuber which regenerates new stems after fire). Xerophytic. Leaves evergreen; (pseudo-) whorled (via closely opposed, decussate pairs); (3–)4 per whorl, or 5 per whorl (in alternating sets); rolled; leathery; imbricate; subsessile, or sessile (without axillary colleters); simple. Lamina entire; linear. Leaves exstipulate. Lamina margins revolute.

Leaf anatomy. Stomata present; anomocytic. Hairs present; eglandular. Complex hairs present; capitate.

Axial (stem, wood) anatomy. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow.

The wood diffuse porous. The vessel end-walls oblique; scalariform and simple. The vessels without vestured pits. The axial xylem without tracheids; without fibre tracheids; with libriform fibres. The parenchyma absent. ‘Included’ phloem absent. Tile cells present. The wood partially storied (the fibres in regular rows).

Reproductive type, pollination. Plants hermaphrodite. Pollination ornithophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary (but crowded on very short, compact, densely leafy, axillary shoots towards the tips of the branches); axillary; (bi-) bracteolate (the bracteoles leaflike, about as long as the calyx); medium-sized; somewhat irregular. The floral irregularity involving the perianth (the calyx). Flowers 5(–6) merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; gamosepalous; five blunt-lobed, or toothed. Calyx lobes about the same length as the tube. Calyx tubular; somewhat unequal but not bilabiate; not persistent; non-accrescent. Corolla 5(–7); 1 whorled; gamopetalous (externally hairy, the lobes distally white-hairy inside). Corolla lobes markedly shorter than the tube. Corolla lobes induplicate valvate; hypocrateriform to tubular (the tube long and narrow, the lobes short); regular; orange and purple, or orange, red, and purple (the lobes purplish black, the tube red or orange).

Androecium 5. Androecial members adnate (near the top of the corolla tube); all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; inserted in the throat of the corolla tube; isomerous with the perianth; oppositisepalous; alternating with the corolla members; shortly filantherous. Anthers deeply sagittate, dorsifixed; dehiscing via longitudinal slits; introrse. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; (constricti-) colporate.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 1–2 celled. Gynoecium syncarpous; synstylovarious; superior. Ovary incompletely 2 locular (completely partitioned below, but the carpellary margins progressively less intruded distally and becoming unilocular above); sessile. Gynoecium stylate. Styles 1 (filiform, persistent); attenuate from the ovary; apical; much longer than the ovary (exserted from the corolla). Stigmas 1–2; 2 lobed. Placentation axile to apical (the ovules in two pairs or trios at the slightly expanded summit of the partial partition). Ovules 2 per locule, or 3 per locule; funicled; pendulous and ascending (one of each pair or trio ascending into the unilocular tip of the ovary, the others descending into their respective semilocules). Hypostase present. Endosperm formation cellular. Endosperm haustoria present.

Fruit non-fleshy; apically, downwardly dehiscent; a capsule. Capsules septicidal and loculicidal (with each of the two valves becoming bifid). Fruit 4–6 seeded. Seeds copiously endospermic. Endosperm not oily (mealy, starchy). Embryo well differentiated. Cotyledons 2. Embryo straight.

Physiology, phytochemistry. Verbascosides detected. Iridoids detected (several, including stilbericoside (cf. Stilbe) and unedoside (cf. Stilbe and Arbutus); ‘Route II’ type (+decarb.).

Geography, cytology. Cape. Sub-tropical. South Africa. 2n = 24. Supposed basic chromosome number of family: 12. 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 Lamiales (as a synonym of Stilbaceae).

Species 1. Genera 1; only genus, Retzia.

General remarks. Close to Buddlejaceae, according to Struwe et al (1994), but exhibiting fewer differences from Scrophulariaceae in terms of the present descriptions. Its nearest neighbours as assessed from the present descriptions are Lamiiflorae rather than Gentianiflorae. The data compiled for Retzia here lack data on anther development and embryology, but depict 8 conspicuous morphological differences from Stilbaceae (q.v.) involving inflorescence, calyx, corolla, androecium, gynoecium and seed. See comments under Loganiaceae.

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: 13th March 2017.’.