Canthium Lam.

Rubiaceae, D. Bridson. Flora Zambesiaca 5:2. 1998

Morphology General Habit

Shrubs or small trees, sometimes scandent; spines absent or present.

Morphology Leaves

Heterophylly sometimes apparent; leaves either deciduous and restricted to brachyblasts (contracted lateral spurs) or apex of stem, or evergreen and spaced along the branches, opposite, paired, petiolate; domatia absent, pit-like or present as tufts of hair; stipules shortly sheathing, apiculate or aristate, glabrous or pubescent within.

Morphology Reproductive morphology Flowers

Flowers hermaphrodite or unisexual, 4–5 merous, pedicellate or not, borne in pedunculate to subsessile few–many-flowered cymes; inflorescence branches present, sometimes reduced; bracteoles inconspicuous.

Morphology Reproductive morphology Flowers Calyx

Calyx tube broadly ellipsoid to ovoid, ± obsolete or somewhat reduced, scarcely equalling the disk, bearing triangular or linear lobes.

Morphology Reproductive morphology Flowers Corolla

Corolla white or yellowish, glabrous or rarely pubescent outside; tube broadly cylindrical, ± equal to lobes or sometimes longer or shorter, with or without a ring of deflexed hairs inside, often pubescent at throat; lobes reflexed or less often erect, obtuse, acute or shortly apiculate.

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens set at throat; anthers subsessile or borne on short filaments, with or without darkened connective tissue on dorsal face.

Morphology Reproductive morphology Flowers Gynoecium

Style slender, shortly exceeding the corolla tube, glabrous; pollen presenter ± spherical, point of attachment within a distinct basal recess, 2(3)-lobed; ovary 2(3)-locular.

Morphology Reproductive morphology Flowers Disc

Disk glabrous (pubescent in some South African species).

Morphology Reproductive morphology Fruits

Fruit a 2(3)-seeded drupe or often 1-seeded by abortion, small to moderately large, strongly dorsiventrally flattened or not, strongly or scarcely indented at apex; pyrenes ellipsoid to ovoid or obovoid, often flattened on ventral face, thinly woody, slightly to distinctly triangular or truncate at point of attachment, with a shallow crest extending to apex, usually rugulose.

Morphology Reproductive morphology Seeds

Seeds with endosperm entire; testa finely reticulate; embryo ± straight to curved with radicle erect; cotyledons small, perpendicular to ventral face of seed.

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution

A genus of 100 species as currently circumscribed, distributed in tropical and southern Africa through Madagascar and the Seychelles to tropical and subtropical Asia, Australia, and the Pacific. Experts have indicated that Canthium sensu stricto does not occur in Papuasia (e.g., see Lantz & Bremer 2004), Australia or the Pacific, but three species are presently known from New Guinea (all endemic): Canthium aurantiacum Merr. & L.M.Perry, C. megistocarpum Merr. & L.M.Perry and C. schlechterianum Merr. & L.M.Perry. It is likely that future studies will see these taxa transferred to either Psydrax, Cyclophyllum or Pyrostria ‘group B’.

Morphology General Habit

Shrubs or small trees to 20 m, sometimes scandent; spines present (then straight) or absent

Morphology General

Raphides absent

Morphology Leaves Stipules

Stipules usually triangular, apex acute to cuspidate, sometimes bent to one side, persistent or not

Morphology Leaves

Leaves chartaceous to sub-coriaceous, domatia present or absent, tertiary venation often obscure

Morphology Reproductive morphology Inflorescences

Inflorescences axillary, pedunculate, cymose, few–many-flowered, inflorescence axes sometimes reduced, bracteoles not easily seen

Morphology Reproductive morphology Flowers

Flowers bi- or unisexual, 4–5-merous, sessile or pedicellate; calyx tube very short to ±absent, with small triangular lobes; corolla valvate, white to yellowish, tube broadly cylindrical, ±equal to lobe length (rarely longer or shorter), throat pubescent or not, lobes reflexed, stamens inserted at throat, filaments short to ±absent, anthers dorso-basifixed, dorsal connective tissue dark or not; ovary 2(–3)-locular, ovules pendulous, 1 per locule; style slightly longer than corolla tube, stigma ±spherical, concave at point of attachment, 2(–3)-lobed

Morphology Reproductive morphology Fruits

Fruit green, ripening to red or orange, a 2(–3)-seeded drupe, or 1-seeded by abortion, bilaterally compressed, or not, often loosely heart-shaped, pyrenes often very hard

Ecology

The New Guinea taxa presently remaining in Canthium are found in forests at low to submontane elevations.

Recognition

The genus is recognisable by the leaves with little tertiary venation, axillary inflorescences, and stipules which often bend to one side. The buds are light-bulb shaped, the stigmas are ±spherical and styles equal to or slightly longer than corolla tube (compared to Psydrax: stigmas narrowly cylindrical, styles much longer than corolla tube). The fruits are often heart shaped and can be very difficult to cut through.

Rubiaceae, B. Verdcourt. Flora of Tropical East Africa. 1976

Morphology General Habit

Shrubs or small trees, sometimes scandent; spines absent or if present straight

Morphology Leaves

Heterophylly sometimes apparent; leaves either deciduous and restricted to brachyblasts or apex of stem, or evergreen and spaced along the branches, opposite, paired, petiolate, papery to subcoriaceous, domatia absent, pit-like or present as tufts of hair; stipules shortly sheathing, apiculate or aristate, glabrous or pubescent within

Morphology Reproductive morphology Flowers

Flowers hermaphrodite or ♀ and ♂, 4–5-merous, pedicellate or not, borne in pedunculate to subsessile few–many-flowered cymes; inflorescence-branches present or reduced; bracteoles inconspicuous

Morphology Reproductive morphology Flowers Calyx

Calyx-tube broadly ellipsoid to ovoid; tubular part of limb ± obsolete or somewhat reduced, scarcely equalling the disk, bearing dentate, triangular or linear lobes

Morphology Reproductive morphology Flowers Corolla

Corolla white or yellowish, glabrous or rarely pubescent outside; tube broadly cylindrical, ± equal to lobes or sometimes longer or shorter, with or without a ring of deflexed hairs inside, often pubescent at throat; lobes reflexed, obtuse, acute or shortly apiculate

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens set at throat; anthers subessile or borne on short filaments, with or without darkened connective tissue on dorsal face

Morphology Reproductive morphology Flowers Gynoecium Pistil

Style slender, shortly exceeding the corolla-tube, glabrous; stigmatic knob ± spherical, point of attachment distinctly recessed, 2(–3)-lobed; ovary 2(–3)-locular

Morphology Reproductive morphology Flowers Disc

Disk glabrous

Morphology Reproductive morphology Fruits

Fruit a 2(–3)-seeded drupe or often 1-seeded by abortion, small to moderately large, strongly dorsiventrally flattened or not, strongly or scarcely indented at apex; pyrenes ellipsoid to ovoid or obovoid, often flattened on ventral face, thinly woody, slightly to distinctly triangular or truncate at point of attachment, with a shallow crest extending to apex, usually rugulose

Morphology Reproductive morphology Seeds

Seeds flattened on ventral face, very shortly crested around apex; endosperm entire; testa finely reticulate; embryo ± straight to curved with radicle erect; cotyledons small, perpendicular to ventral face of seed.

Rubiaceae, D. Bridson. Flora Zambesiaca 5:2. 1998

Morphology General Habit

Shrubs or small trees; armed with spines setabove brachyblasts (reduced lateral branches).

Morphology Leaves

Leaves restricted to lateral branches, paired but congested, petiolate; domatia present; stipules small, connate at the base, with silky white hairs inside, soon caducous.

Morphology Reproductive morphology Flowers

Flowers 4-merous, borne in pedunculate corymbose cymes; bracts and bracteoles inconspicuous.

Morphology Reproductive morphology Flowers Calyx

Calyx tube ± ovate; limb short, repand or shortly toothed.

Morphology Reproductive morphology Flowers Corolla

Corolla creamy-white; tube cylindrical, somewhat shorter than the lobes, densely choked with moniliform hairs at the throat; lobes reflexed, thickened but not apiculate at the apex.

Morphology Reproductive morphology Flowers Androecium Stamens Anthers

Anthers distinctly exserted, but not reflexed.

Morphology Reproductive morphology Flowers Gynoecium Style

Style narrowly cylindrical, slightly more than twice the length of the corolla tube.

Morphology Reproductive morphology Flowers Pollen

Pollen presenter very slightly longer than broad, hollow at the base, 3-lobed at the apex.

Morphology Reproductive morphology Flowers Disc

Disk not markedly prominent, glabrous.

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary 3(4)-locular; ovule 1 per loculus, attached near apex to the septum.

Morphology Reproductive morphology Fruits

Fruit a 1–3(4)-seeded, fleshy drupe.

Morphology Reproductive morphology Fruits Pyrene

Pyrenes flattened ellipsoid, clearly crested around the apex.

Morphology Reproductive morphology Seeds

Seeds flattened ellipsoid, ± winged at the apex, very finely reticulate; embryo slightly curved with an erect radicle, and small cotyledons oriented ventrally to face of seed.