REVISION OF SCHIZOMUSSAENDA ( RUBIACEAE )

Mussaenda L. is a large paleotropical genus of Rubiaceae, and its circumscription has always been controversial between different authors (Miquel 1857, Hooker 1880, Kurz 1887, Wernham 1916, Li 1943, Alejandro et al. 2005). Recently, Alejandro and collaborators (2005) conducted phylogenetic analyses based on ITS and trnT-F sequence data, suggesting a new circumscription of Mussaenda s.s with c. 132 species and endorsing a close relationship of Mussaenda to Schizomussaenda, Pseudomussaenda and Neomussaenda (Tange 1994). Schizomussaenda was established by Li (1943), based on a sole species, S. dehiscens (Craib) H.L.Li. This species had been previously described as Mussaenda dehiscens Craib (1916). The diagnostic characters of this monotypic genus include its loculicidally 2-valved capsular fruit, dehiscing at the top, the elongated scorpioid-cymose inflorescence, and the long petiole of petaloid calyx-lobe (Fig. 1). Otherwise it is similar to other Mussaenda species in floral and gross morphology. Most recent studies on Rubiaceae recognize its generic status (Puff et al. 1993, Tange 1994, Bremer & Thulin 1998, Alejandro et al. 2005).


INTRODUCTION
Mussaenda L. is a large paleotropical genus of Rubiaceae, and its circumscription has always been controversial between different authors (Miquel 1857, Hooker 1880, Kurz 1887, Wernham 1916, Li 1943, Alejandro et al. 2005).Recently, Alejandro and collaborators (2005) conducted phylogenetic analyses based on ITS and trnT-F sequence data, suggesting a new circumscription of Mussaenda s.s with c. 132 species and endorsing a close relationship of Mussaenda to Schizomussaenda, Pseudomussaenda and Neomussaenda (Tange 1994).
Schizomussaenda was established by Li (1943), based on a sole species, S. dehiscens (Craib) H.L.Li.This species had been previously described as Mussaenda dehiscens Craib (1916).The diagnostic characters of this monotypic genus include its loculicidally 2-valved capsular fruit, dehiscing at the top, the elongated scorpioid-cymose inflorescence, and the long petiole of petaloid calyx-lobe (Fig. 1).Otherwise it is similar to other Mussaenda species in floral and gross morphology.Most recent studies on Rubiaceae recognize its generic status (Puff et al. 1993, Tange 1994, Bremer & Thulin 1998, Alejandro et al. 2005).

MATERIALS AND METHODS
More than one hundred collections of herbarium specimens from GXMI, HITBC, IBK, IBSC, K, KUN, L, P and PE, including the type specimens of both Mussaenda henryi and M. elongata, and most of the original materials cited in Li (1943) were examined.The type of Schizomussaenda dehiscens, despite all the efforts, however, has not been able to be located.Ten individuals per population were randomly collected to observe and measure plant size, leaf size and shape, petaloid calyx-lobe size and shape, corolla-tube length, style and stigma length, and stamen height.

RESULTS
During our field works in Yunnan Province, we found that Schizomussaenda dehiscens (Fig. 1) is a locally abundant species.The measurement data derived from field notes and observations revealed that the genus is distylous.Within the same population of S. dehiscens, it is variable in plant height (2-8 m tall), shape and size of the leaf and petaloid calyx-lobe.The leaf shape varies from ovate, narrowly ovate, to elliptic or narrowly elliptic (10-25 by 2.5-8 cm).The leaf base is rounded, attenuate or cuneate.The petaloid calyx-lobe is ovate with attenuate or rounded base (6-11 cm long) and the petiole is 1.7-3.5 cm long.In short-styled (thrum) flowers the length of the corolla-tube is 2.3-2.85cm, the length of the style/stigma is 1.87-2.55cm, and the height of the stamen is 2.7-3.13cm.In long-styled (pin) flowers the length of corolla-tube, style/ stigma and stamens are 2.55-3.1,2.63-3.46 and 2.22-3.12cm long, respectively.
The type specimens of Mussaenda henryi (Fig. 2) and M. elongata (Fig. 3) are indistinguishable from specimens identified as Schizomussaenda dehiscens (Fig. 4) in floral  characters but the shape and size of the leaves and petaloid calyx-lobes.The leaves of Mussaenda henryi are elliptic or narrowly elliptic with rounded base, up to 10-15 by 4-6 cm and the white petaloid calyx-lobes are ovate with rounded base, up to 7-10 by 4.5-7 cm (with petiole 2-2.5 cm long), whereas in M. elongata, the leaves are narrowly elliptic with attenuate base, up to 18-24 by 5-7 cm and the white petaloid calyx-lobes are narrowly ovate with attenuate base, up to 8-12 by 4-5 cm (with petiole 3-3.5 cm long).But according to our field studies mentioned above, the difference between M. henryi and M. elongata, and between each of them to Schizomussaenda dehiscens, falls well within the range of variation of S. dehiscens within a single population.Although all two type specimens lacked fruits, the elongated scorpioid-cymose inflo- rescence and floral characters all demonstrate well their Schizomussaenda characteristics.The type specimens of M. henryi and M. elongata are indeed conspecific with Schizomussaenda dehiscens.Therefore, the three names are reduced to one.Because the name Mussaenda henryi has priority over both M. elongata and M. dehiscens, a new combination, Schizomussaenda henryi (Hutch.)X.F.Deng & D.X.Zhang, is proposed, and the other two names, M. elongata and M. dehiscens, are reduced to its synonymy.

Field
studies were carried out at Xishuangbanna Tropical Botanical Garden and along Xiaola Highway, Mengla County, Yunnan Province (China) in 2005 and 2006.We sampled three populations of Schizomussaenda dehiscens, one population at Xishuangbanna Tropical Botanical Garden (voucher: X.F.Deng & H. Ren 400) and the others both along Xiaola Highway in Xishuangbanna (voucher: X.F.Deng & H. Ren 442, X.F.Deng & L. Gu 513).