Dasus Loureiro; Litosanthes Blume; Mephitidia Reinwardt ex Blume.

Erect subshrubs, shrubs, or rarely small trees, unarmed, with tissues sometimes fetid. Branches and branchlets terete, sometimes compressed, rarely fistulous; lenticels inconspicuous or conspicuous. Raphides present. Leaves opposite, distichous, usually thinly leathery or papery, base acute to rounded or cordate, apex acuminate, acute or cuspidate; midrib plane, depressed or slightly prominent adaxially, usually prominent abaxially; veins generally prominent abaxially, ascending at an angle of more than 45°, curved to margin or joining nerves above at margin; tertiary nervules parallel or reticulate; stipules caducous or usually persistent at least near stem apex, interpetiolar, well developed or reduced, triangular, lanceolate, ovate, or oblong, acute or obtuse. Inflorescence axillary, several flowered and glomerulate, capitate, cymose, or with flowers solitary, sessile or pedunculate, ebracteate or bracteate with bracts persistent or not, well developed, sometimes fused. Flowers bisexual, small, sessile or pedicellate. Calyx with hypanthium portion obovoid, ovoid, or campanulate; limb 3-6-dentate or lobed or rarely truncate. Corolla white, funnelform or salverform to urceolate (Lasianthus biflorus), from several millimeters long up to 2.5 cm, glabrous or hairy outside, inside glabrous or usually villous in throat; lobes 4-6, valvate or imbricate in bud. Stamens 4-6, inserted in corolla throat; filaments short; anthers linear or oblong, dorsifixed, included or exserted. Style linear; stigma lobes 3-9, linear or lanceolate, included or exserted. Ovary 3-9-celled, ovules 1 in each cell, basal, erect. Fruit blue or rarely white, black, or red, drupaceous, small, pulpy or fleshy, usually globose, smooth or warty, rounded or ridged, with calyx limb persistent; pyrenes 3-9 (sometimes fewer than that developing), thick walled, smooth, warty or sulcate on abaxial face, usually triangular in transverse section, with preformed germination slits; seed black, with abundant endosperm; embryo straight; cotyledon short, flattened; radicle long clavate.

Lasianthus is commonly collected in China. This genus has been studied in detail by H. Zhu for both China (Acta Phytotax. Sin. 32: 49-81. 1994; Syst. & Geogr. Pl. 72: 63-110. 2002; Acta Bot. Yunnan. 30: 308-314. 2008) and Thailand (Acta Phytotax. Sin. 39: 116-150. 2001: 53 species included). As Zhu detailed (loc. cit. 2002: 63), the characters that distinguish species of Lasianthus are mostly small and/or subtle, frequently ephemeral, and often difficult to see; and, consequently, the taxonomy of this genus is complicated. Lasianthus can be confused with some species of Damnacanthus, Diplospora, Prismatomeris, Saprosma, and Urophyllum, especially when collected only with young flower buds. Lasianthus (Chinese species) is rather distinctive vegetatively in its combination of leaf blades that are completely glabrous adaxially, petioles that are usually densely pubescent even when other parts of the plant are glabrescent or only sparsely pubescent, and small stipules that are usually persistent and also densely pubescent.

The leaf venation of Lasianthus frequently has a characteristic regular pattern, comprising subparallel or exceptionally regularly oriented tertiary veins ("nervules"). This is different, however, from the lineolate quaternary venation found in Antirhea, Timonius, and some other genera. A similar arrangement is found in some species of Urophyllum. Cai et al. (Acta Bot. Yunnan. 29: 497-512. 2007) studied leaf details of Lasianthus and [broadly] related genera, and Cai et al. (J. Syst. Evol. 46(1): 62-72. 2008) studied the pollen of a similar group.

The genus Litosanthes has been variously treated as a genus with one to several species, or included in Lasianthus. H. S. Lo (in FRPS 71(2): 106-108. 1999) treated Litosanthes as a separate genus of one or two species, as did Puff et al. (Rubiaceae of Thailand, 102. 2005). However, H. Zhu (loc. cit. 2002: 69) included it as a synonym of Lasianthus, as done here, based on morphological and molecular evidence.

Lasianthus verrucosus H. S. Lo (Bot. J. S. China 2: 2. 1993; type specimen: China. Hainan: Ledong, Q. Huang 820468, SCBI) was not seen. From H. S. Lo’s description and figure of this species, it has leaves with a looped venation, glabrous and fuscous when drying; inflorescence sessile or subsessile; calyx limb with 4 small, broadly triangular lobes; and pyrenes 4, verrucose on the abaxial face. Many Lasianthus specimens from Hainan were examined, but none was found matching the description of L. verrucosus. Consequently, this species is excluded from this account. From the original description it appears to be most similar to Saprosma merrillii and thus would likely key out as that species.

The phylogenetic relationships among species of Lasianthus and related genera were studied based on molecular data by Xiao and Zhu (Bot. Stud. (Taipei) 48: 227-232. 2007). Their results supported the inclusion of Litosanthes biflora and Saprosma crassipes within Lasianthus. Litosanthes is accordingly included here. However, S. crassipes has a 2-locular ovary and 2-pyrene drupes, which do not match the current circumscription of Lasianthus. Saprosma merrillii seems similar to S. crassipes, and their systematic position needs further study.

Lasianthus cyanocarpus Jack was reported from China by the Flora of Japan. However, true L. cyanocarpus has a restricted distribution in S Thailand and Malesia. This name is therefore misapplied in China and Japan, where the correct name for the species is L. hirsutus.

The following species was recorded from China but could not be treated here because no material was seen by the present authors: Lasianthus areolatus Dunn (J. Bot. 47: 376. 1909), recorded from Guangdong by Merrill and Chun (Sunyatsenia 1(1): 49. 1930).

About 184 species: 160 species in tropical Asia, ca. 20 in Africa, three in tropical America, and one in Australia; 33 species (seven endemic) in China.

(Authors: Zhu Hua (朱华); Charlotte M. Taylor)