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Annual herbs or herbaceous shrubs. Leaves spirally arranged, 3-5 nerved from the base, serrulate, with entire or lobed margin. Inflorescence cymes, opposite the leaf. Flowers hermaphrodite, 5-merous. Sepals free, hairy outside, glabrous inside. Petals free, united in a tube when young, glabrous, glandular at the base. Stamens free, anthers dorsifixed, subglobose, opening lengthwise, staminode absent. Ovary 2-5 locular, each locule with 2 ovules, styles subulate, stigmas pointed. Fruit a capsule, wingless, not lobed, pericarp spiny, indehiscent.

Key to the species

Serial Key Reference
1a. Stems glabrous except for alternating line of hairs on internodes; capsules and spines on capsules glabrous T. annua
1b. Stems hairy all around; capsules pubescent or tomentose; spines on capsules glabrous or hairy 2
2a. Spines glabrous T. rhomboidea
2b. Spines pubescent or tomentose 3
3a. Spines straight. Leaves ovate-oblong; stamens 10-12, capsules more than 10 mm across T. obliqua
3b. Spines uncinate 4
4a. Capsules more than 6 mm across T. pilosa
4b. Capsules up to 5 mm across. Leaves rhomboid-ovate, 3-lobed or entire, spines with a line of hairs T. pentandra