Herbs, annual or perennial, or subshrubs, unarmed. Raphides present. Leaves opposite, sometimes clustered and appearing whorled, rosulate, or pseudoverticillate, isophyllous to anisophyllous, without domatia; stipules persistent to caducous, interpetiolar, triangular, entire to 2(-5)-lobed. Inflorescences terminal and/or pseudoaxillary, cymose to paniculiform with axes slender and dichasial or often scorpioid, several to many flowered, pedunculate, bracteate or bracts reduced. Flowers sessile to pedicellate, bisexual, usually if not always distylous. Calyx with ovary portion usually 5-ridged or -winged, limb 5-lobed. Corolla white, pink, purple, or red, campanulate, funnelform, urceolate, or tubular, inside usually pubescent in throat and with pubescent ring near middle; lobes 5, in bud valvate or induplicate-valvate, often winged or keeled dorsally, sometimes notably pinnatinerved. Stamens 5, inserted below middle of corolla tube and included in long-styled flowers, inserted in throat or middle of corolla tube and partially exserted in short-styled flowers; filaments short to developed; anthers dorsifixed. Ovary 2-celled, ovules numerous in each cell on peltate axile placentas attached to middle of septum; stigmas 2-lobed, included to shortly exserted in long-styled flowers, included and positioned near middle of corolla tube in short-styled flowers. Fruit capsular, subglobose, often 5-ridged to -winged, with apical portion prolonged into beak, dehiscing loculicidally and often also simultaneously or subsequently septicidal from top, dividing partially to completely into 2 or 4 valves with walls usually persistent, papery to stiff, with calyx limb persistent, sometimes elongating; seeds numerous, small, angled; testa reticulate or alveolate; embryo minute; endosperm fleshy.

Robbrecht (Opera Bot. Belg. 1: 1-271. 1988; Opera Bot. Belg. 6: 1-200. 1993) accepted earlier conclusions that Spiradiclis is related to Ophiorrhiza; a more recent study based on molecular data suggests that the situation may be more complex and calls into question the separation of these genera (Rydin et al., Pl. Syst. Evol. 278: 101-120. 2009). H. S. Lo (in FRPS 71(1): 86. 1999) described the corolla lobes as valvate in bud, but they were described as induplicate-valvate by Bakhuizen f. (Fl. Java 2: 289. 1965). This genus does not appear to be well known at all. It has only been studied regionally, in particular by H. S. Lo et al. (Acta Bot. Austro Sin. 1: 27-36. 1983), H. S. Lo (Bull. Bot. Res., Harbin 6(4): 31-53. 1986), Deb and Rout (Candollea 44: 225-229. 1989), H. S. Lo (Bull. Bot. Res., Harbin 18: 275-283. 1998), and R. J. Wang (Novon 12: 420-423. 2002). Ma et al. (J. Trop. Subtrop. Bot. 13(3): 264-270. 2005) studied seed morphology of sixteen Spiradiclis species and found partial correlation with the infrageneric classification of Lo.

H. S. Lo (loc. cit. 1998: 275-276) recognized two subgenera, distinguished as follows:

Spiradiclis subg. Spiradiclis: ellipsoid to linear-oblong capsules that are 2-4 × as long as wide and have straight valves, including eight (or possibly nine or ten) species in China;

Spiradiclis subg. Sinospiradiclis H. S. Lo: subglobose capsules that are ± as long as wide and have the valves ultimately twisted, including the remaining Chinese species.

One subsequently described species, Spiradiclis chuniana R. J. Wang, was not classified to subgenus when it was published because the fruit were unknown. The key here follows that of H. S. Lo in FRPS (71(1): 86-88. 1999), apparently intended as a schematic outline of the genus classification, with some changes: here the full range of variation that is given in the descriptions has been added to the key leads, and a few species have been moved to different sections within the key based on Lo’s descriptions. This key does not fully distinguish all the species; however, it cannot be improved on with the information now available and is here presented to summarize in English the existing information on Chinese Spiradiclis and to highlight problematic areas of its taxonomy.

At least 40 species: Bhutan, China, India, Indonesia, Myanmar, Vietnam; 35 species (31 endemic, one of unconfirmed occurrence) in China.

(Authors: Chen Tao (陈涛); Charlotte M. Taylor)