Family Myrothamnaceae

Myrothamnaceae Niedenzu

Habit and leaf form. Small shrubs (with rigid, opposite branches); resinous (from cells in the leaf epidermis). Xerophytic. Leaves small; opposite; flat, or folded (blackening and folding fanlike when dry, expanding and greening again after rain); more or less connate (the petiole bases of the opposite leaves sheathing); aromatic; simple. Lamina entire; oblong, or obovate (cuneate-flabellate or narrowly elliptic, toothed across the broadly rounded apex); palmately veined; without cross-venules. Leaves stipulate. Stipules intrapetiolar (subulate, on the sheathing petiole bases); free of one another; persistent (with the petioles). Lamina margins apically dentate. Vernation plicate.

Leaf anatomy. Stomata present; anomocytic.

The mesophyll containing calcium oxalate crystals. The mesophyll crystals druses.

Stem anatomy. Cortical bundles absent. Medullary bundles absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids; with vessels. Vessel end-walls oblique; scalariform, or reticulately perforated. Primary medullary rays narrow (uniseriate). Wood parenchyma apotracheal.

Reproductive type, pollination. Plants dioecious. Gynoecium of male flowers absent. Floral nectaries absent. Pollination anemophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes, or in catkins. Inflorescences erect spikes or catkins. Flowers bracteate; regular; cyclic. Hypogynous disk absent.

Perianth absent.

Androecium 4, or 3–8. Androecial members free of one another (and 4), or coherent (when 3–8, then connate by their filaments). Androecium of male flowers, exclusively of fertile stamens. Stamens 3–8 (with large anthers). Anthers basifixed; non-versatile; dehiscing via longitudinal slits (? — not by valves); latrorse; more or less appendaged. The anther appendages apical (representing a small apical prolongation of the connective). Endothecium developing fibrous thickenings. Pollen shed in aggregates; in tetrads. Pollen grains aperturate; 3 aperturate; weakly colpate; 2-celled.

Gynoecium 3–4 carpelled. The pistil 3–4 celled. Gynoecium syncarpous; synovarious; superior. Ovary 3–4 locular. Gynoecium stylate. Styles 3–4; free; short, broad, recurved. Stigmas 3–4 (ventral, decurrent). Placentation axile. Ovules 10–50 per locule (‘rather numerous’); funicled; horizontal; biseriate; anatropous; bitegmic; crassinucellate. Endosperm formation nuclear.

Fruit non-fleshy; a schizocarp. Mericarps 3–4; comprising follicles (the carpels separating septicidally and opening ventrally). Seeds copiously endospermic. Endosperm oily. Seeds minute, or small. Embryo well differentiated. Cotyledons 2.

Physiology, biochemistry. Not cyanogenic. Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid present.

Geography, cytology. Paleotropical. Tropical. Southern tropical Africa, Madagascar. 2n = 20.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Hamamelidales. Cronquist’s Subclass Hamamelidae; Hamamelidales. APG 3 core angiosperms; core eudicot (informal group above Superorder not specified); Superorder Myrothamnanae; Order Gunnerales.

Species 2. Genera 1; only genus, Myrothamnus.