The genus Sauropus
Blume (Blume, 1825
) contains monoecious and dioecious woody herbs to small shrubs. Most of the species commonly occur in monsoonal tropical woodlands and rain forests (Van Welzen, 2003
is closely related to Breynia
. Distinguishing morphological characters are not always clear-cut for these genera.
Molecular phylogenetic studies of Phyllanthus
, the largest genus in Phyllanthaceae, found three out of its eight subgenera to be polyphyletic and the genus in its traditional circumscription to be paraphyletic (Kathriarachchi et al., 2005
are embedded in Phyllanthus
. If all these genera are united with Phyllanthus
, then the number of Phyllanthus
species increases from 833 to 1269 (Govaerts et al., 2000
) and a giant and morphologically heterogeneous genus is created. Many nomenclatural changes would be necessary to obtain a classification that conforms to the molecular results. Kathriarachchi et al. (2005
) suggested the possibility of maintaining a paraphyletic Phyllanthus
or recognizing >20 clades in Phyllanthus
at generic rank. However, Hoffmann et al. (2006)
argued for uniting Phyllanthus sensu lato
) and avoiding a paraphyletic construct. The non-monophyletic subgenera and problem genera deeply embedded within Phyllanthus
are in need of analysis to resolve the issues of the Phyllanthus
is one of these problem genera (morphologically difficult to recognize; e.g. Van Welzen, 2000
) apparently deeply embedded within Phyllanthus
(Kathriarachchi et al., 2006
). Traditionally the genus was classified in Euphorbiaceae subfamily Phyllanthoideae (Webster, 1994
; Radcliffe-Smith, 2001
). Later, Euphorbiaceae was segregated into five families based on molecular phylogenetic studies (APG II, 2003
is now placed in Phyllanthaceae (Wurdack et al., 2004
; Kathriarachchi et al., 2005
; Samuel et al., 2005
; Hoffmann et al., 2006
). The genus comprises 83 species found in the Mascarenes, India, south-east Asia, Malesia and Australia (Govaerts et al., 2000
; Van Welzen, 2003
). There are two centres of diversity, one in Thailand–Indochina, Sauropus sensu stricto
), and one in Australia, where most species formerly placed in Synostemon
(Airy Shaw, 1980a
; Radcliffe-Smith, 2001
; Van Welzen, 2003
) are found. Here Sauropus s.l.
is used for the combination of south-east Asian Sauropus
, Sauropus s.s.
for the mainly south-east Asian part of Sauropus
for the mostly Australian species.
The placement of Synostemon
has long been under doubt. Airy Shaw (1980a)
considered these genera to resemble each other closely in habit, with the differences between them supposedly too small to recognize both groups at the generic rank (Airy Shaw, 1971
). He stated (1980a
): ‘Their bifocal development in Southeast Asia and Australia is curious and without an obvious parallel. It does not seem possible to utilize the subgenera and sections proposed by Müller Arg.…(1866)
and by Pax & Hoffmann…(1922)
, in order to systematize the genus as a whole, including the Australian species. The so-called section (or subgenus) Hemisauropus
Müll.Arg. (cf. Kew Bull. 23:55 (1969)) appears to be unrepresented in Australia, and is in any case doubtfully tenable as a natural group, since the distinctive floral character seems to be uncorrelated with vegetative or other features’. Airy Shaw suggested placing the Australian species into section Schizanthi
, but at the same time he noted the increased morphological problems within this section. Radcliffe-Smith (2001)
stated that Airy Shaw might have a good reason for transferring the Australian species of Synostemon
. However, he also indicated the problematic demarcation of Sauropus
, because the latter resembles Synostemon
in floral characters.
The presence of diploporate pollen suggests a close relationship between Sauropus s.l.
(Sagun and Van der Ham, 2003
), and there is also a great resemblance in seed morphology (Stuppy, 1996
; Tokuoka and Tobe, 2001
). A phylogenetic study based on morphological and palynological data showed Sauropus
to be paraphyletic with diploporate Phyllanthus
species embedded within the genus, and Sauropus s.s.
distinct from Synostemon
(Van Welzen, 2003
; Hunter, 2005
). Only one species formerly included in Synostemon
, Sauropus bacciformis
(L.) Airy Shaw, was found to be better placed within Sauropus s.s.
of south-east Asia. Breynia
formed a polytomy with two groups of Sauropus
. However, Van Welzen (2003)
found no bootstrap support for these results. More recently molecular phylogenetic studies by Kathriarachchi et al. (2006)
confirmed the paraphyletic nature of Sauropus
, with Breynia
embedded in the largely unresolved Sauropus
. The sample of Sauropus
species used by Kathriarachchi et al.
was insufficient to confirm the separation of the south-east Asian Sauropus
. Further molecular work is needed to clarify relationships in and around Sauropus
. Here, molecular phylogenetic analyses were carried out using nuclear and plastid DNA markers to elucidate the limits of Sauropus
, and to confirm its position within Phyllanthaceae.