Vasilis Teodoridis:
RUBIACEAE/Canthium
Canthium horridum Bl. Bijdr. 966. 1826.
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Shrubs; 2--3 m tall; armed with thorns; branchlets slender; terete; appressed dust-yellow soft hairy; thorns 3--30 mm long; opposite; axillary; straight; sharp. Petioles short; 2--3 mm long; slightly soft hairy; leaf blade ovate or elliptic; 2--5 x 1--2 cm; papery; apex obtuse; acute or sub-acuminate; base rounded or broadly cuneate; glabrous or slightly soft hairy along midrib; lateral veins 2--3 pairs; slender; slightly distinct abaxially; stipules 2--3 mm long; hairy/pubescent?. Flowers small; sessile or shortly pedicellate; solitary or several clustered in axils of leaves; bracteoles cupulate?; attached at top of pedicels. Calyx tube obconical; 1--1.5 mm; apex with minute; undulate teeth. Corolla white; tube short; suburceolate; ca. 2 mm long; glabrous abaxially; retrorsely bearded at corolla throat; lobes 5; oblong; ca. 3 mm; apex acute. Filaments short; anthers included or slightly exserted; ca. 5 mm long; soft hairy at base. Stigma fusiform; scabrous. Drupes ovoid; solitary or binate/didymous; 1.5--2.5 cm long; 1--2 cm in diameter; apex with minute persistent calyx limb; with 1 or 2 pyrenes; pyrenes indistinctly tuberculate. Fl. Apr--Jun; fr. Jul--Nov.
Thickets at low elevation. Guangdong; Hong Kong; Hainan; Guangxi; Yunnan [India; Indo-China; Malesia].