Habit and leaf form. Small trees, or shrubs (the branchlets sometimes spiny). Plants non-succulent. Leptocaul. Leaves alternate; spiral; non-sheathing; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire.
Stem anatomy. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with vessels. Vessel end-walls simple. Sieve-tube plastids P-type; type III (a).
Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Plants dioecious. Female flowers without staminodes. Gynoecium of male flowers absent.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, or in racemes, or in fascicles, or in panicles. The ultimate inflorescence unit cymose. Inflorescences small, branched cymes, racemes, panicles or fascicles. Flowers bracteate; small. Free hypanthium absent.
Perianth sepaline; 4, or 5; 1 whorled; green. Calyx 4, or 5; 1 whorled; polysepalous; regular; persistent; imbricate.
Androecium in male flowers, 10–20. Androecial members free of the perianth; coherent (basally connate); 1 adelphous. Androecium exclusively of fertile stamens. Stamens 10–20. Anthers basifixed (elongate-oblong); non-versatile; dehiscing via longitudinal slits; extrorse. Pollen grains aperturate (the apertures poorly defined, irregular in shape and distribution); 4–7 aperturate; foraminate, or rugate, or colpate (Phaulothamnus); spinulose.
Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synovarious (the styles simple, divergent, uncinate); superior. Ovary 1 locular. Gynoecium stylate. Styles 2. Stigmas 2. Placentation basal. Ovules in the single cavity 1; funicled; ascending; non-arillate; campylotropous.
Fruit fleshy; indehiscent; a berry. Dispersal unit the fruit. Fruit 1 seeded. Seeds (strictly) non-endospermic.
Perisperm present (copious, mealy). Embryo well differentiated. Cotyledons 2. Embryo curved.
Physiology, biochemistry. Ellagic acid absent.
Geography, cytology. Sub-tropical to tropical. Warm America.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Caryophylliflorae; Caryophyllales. Cronquist’s Subclass Caryophyllidae; Caryophyllales. APG (1998) Eudicot; core Eudicot; neither Rosid nor Asterid. APG 3 (2009) Order: Caryophyllales.
Species 10. Genera 2; Achatocarpus, Phaulothamnus.
• Technical details (Achatocarpus).