Description from Flora of China
Blechum P. Browne; Cryphiacanthus Nees; Dipteracanthus Nees.
Herbs [or shrubs], perennial, prostrate to erect, with cystoliths. Leaves sessile or petiolate; leaf blade margin entire, crenulate, or dentate. Inflorescences axillary or terminal, reduced or expanded dichasia, sometimes forming dichasiate spikes, thyrses, or panicles, sometimes reduced to a solitary flower; bracts opposite, usually green, margin entire; bracteoles 2 [or absent]. Flowers [sessile or] subsessile to pedicellate. Calyx deeply 5-lobed; lobes equal or subequal. Corolla funnel-shaped; tube basally with a narrowly cylindric portion, usually expanded apically into a distinct throat; limb 5-lobed; lobes usually ovate to orbicular, equal to unequal in size, contorted in bud. Stamens 4, didynamous, usually included in corolla tube; filaments sometimes connate in pairs at base; anthers 2-thecous; thecae equal, parallel to subsagittate, muticous at base; staminode 1 or absent. Ovary with up to 10 ovules per locule; style usually included in corolla tube or slightly exserted; stigma 2-lobed, lobes equal or unequal. Capsule stipitate or not stipitate, [4-]12-26-seeded; retinacula present; septa with attached retinacula remaining attached (or separating in Ruellia blechum) to inner wall of mature capsule. Seeds discoid, usually pubescent with hygroscopic trichomes.
Blechum and Dipteracanthus are included in Ruellia based on morphological and molecular data (C. Ezcurra, Ann. Missouri Bot. Gard. 80: 787-845. 1993; E. Tripp, Syst. Bot. 32: 628-649. 2007; E. Tripp et al., Taxon 58: 893-906. 2009).
About 250 species: tropical to temperate regions worldwide; four species (one endemic, two introduced) in China.
(Authors: Hu Jiaqi (胡嘉琪 Hu Chia-chi), Deng Yunfei (邓云飞); Thomas F. Daniel)