Canthium Lam.

Scientific Description

Family Rubiaceae.

Habit and leaf form. Trees, or shrubs; evergreen, or deciduous. Plants spiny (thorns axillary), or unarmed. Young stems tetragonal. Self supporting, or climbing (sometimes). Helophytic, or mesophytic, or xerophytic. Leaves minute to large; opposite; papery to subcoriaceous; petiolate; connate (via the stipules), or not connate; gland-dotted, or not gland-dotted; simple; epulvinate. Leaf blades entire; pinnately veined; cross-venulate. Leaves with stipules. Stipules interpetiolar (shortly sheathing, apiculate or aristate); with colleters (secreting mucilage), or without colleters. Leaf blade margins entire, or serrate. Leaves without a persistent basal meristem. Domatia recorded; represented by pits, or hair tufts. Leaf anatomy. Hairs absent. Stem anatomy. Nodes unilacunar, or tri-lacunar. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite, or functionally male and functionally female. Unisexual flowers present, or absent. Plants hermaphrodite, or monoecious, or dioecious. Plants homostylous, or heterostylous. Entomophilous. Pollination mechanism conspicuously specialized (with passive pollen presentation involving stylar modification), or unspecialized.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’, or solitary (rarely). Inflorescence few-flowered to many-flowered. Flowers in cymes (or clusters), or in panicles (a thyrse). The terminal inflorescence unit cymose. Inflorescences axillary. Flowers bracteolate. Bracteoles inconspicuous. Flowers small to medium-sized; regular; 4–6 merous; cyclic; tetracyclic. Free hypanthium present, or absent (depending on interpretation); cup-shaped, obovoid or globular. Perianth with distinct calyx and corolla; 8–12; 2 -whorled; the two whorls isomerous. Calyx 4–6; 1 -whorled; gamosepalous; lobed (with 4–6 teeth); glabrous, or hairy (minutely pubescent); open in bud; regular; persistent. Corolla 4–6; 1 -whorled; gamopetalous; valvate; tubular; regular; hairy abaxially, or glabrous abaxially; hairy adaxially (hairy inside mouth), or glabrous adaxially; white to cream, or yellow; deciduous. Corolla lobes narrowly oblong. Fertile stamens present, or absent (when flower female). Androecium 4, or 5. Androecial members adnate (to the corolla tube); free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 4, or 5; becoming exserted (usually); isomerous with the perianth; oppositisepalous. Anthers dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged. The anther appendages apical. Pollen shed in aggregates, or shed as single grains; if aggregated, in tetrads. Fertile gynoecium present, or absent (when flower male). Gynoecium 2(–3) carpelled. The pistil 2(–3) celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylovarious to eu-syncarpous; inferior. Ovary plurilocular; 2(–3) locular. Gynoecium transverse. Epigynous disk present. Gynoecium stylate. Styles 1 (apically ovoid or mitre-shaped); attenuate from the ovary, or from a depression at the top of the ovary; apical; shorter than the ovary at anthesis to much longer than the ovary at anthesis; becoming exserted; deciduous. Stigmas 1; 1–2(–3) - lobed; wet type, or dry type; papillate, or non-papillate; Group II type and Group IV type. Placentation axile. Ovules 1 per locule; pendulous, or horizontal; anatropous, or hemianatropous.

Fruit and seed features. Fruit fleshy; indehiscent; a drupe (globular, with compressed sides or divided into 2 equal parts attached along the middle). The drupes with one stone, or with separable pyrenes (pyrenes 2). Fruit 2–3 seeded, or 1 seeded (by abortion). Seeds endospermic. Endosperm ruminate, or not ruminate; oily. Cotyledons 2. Embryo straight, or curved. Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, biochemistry. Aluminium accumulation demonstrated, or not found.

Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, and Queensland. Northern Botanical Province and Eremaean Botanical Province.

Additional comments. It is likely that Australian species of this genus will be transferred to the genus Psydrax (James 1992c).

Additional characters Corolla lobes spreading.

Etymology. From Canti, name of one species in Malabar.