Previous generic placements of Thamnocalamus tessellatus were based upon an incomplete knowledge of its morphology. Nastus tessellatus Nees was described before its flowers were known, and transferred into Arundinaria (Munro 1868) simply as it bore “very great resemblance” to that genus. Later discovery of its flowers has shown that it indeed has 3 stamens, rather than the 6 of Nastus, but it has pachymorph rhizomes (see Stapleton 1997: fig. 1) rather than the leptomorph rhizomes of Arundinaria.

It was transferred into Thamnocalamus largely on the basis of leaf anatomical characters by Soderstrom and Ellis (1982), who found that Arundinaria tessellata shared 10 characters out of 11 with Thamnocalamus spathiflorus (Trin) Munro, while it only shared 7 characters with Fargesia nitida (Mitford) Keng f. However, Arundinaria tessellata also shared only 5 characters with Thamnocalamus aristatus E.G. Camus, while the possibly conspecific Thamnocalamus spathiflorus and Thamnocalamus aristatus themselves only shared 6 out of 11 characters. When morphological characters other than those of leaf anatomy, along with more recent molecular results are taken into account, it would appear that the anatomical characters used by Soderstrom and Ellis (1982) are more informative at the level of species or below rather than at generic level.

The synflorescence of Thamnocalamus tessellatus has been well illustrated in Hooker’s Icones Plantarum (Prain 1913: Tab 2930 http://www.botanicus.org/page/1349516), and by Soderstrom and Ellis (1982). When examined closely, it can be seen that the synflorescence of Thamnocalamus tessellatus has similarities to those of both Thamnocalamus and Fargesia Franchet, see Table 1, as they are compressed, and are associated with several supporting sheaths. However, while Thamnocalamus has loose racemose panicles, Thamnocalamus tessellatus, like Fargesia, consistently bears short racemes. These are structurally very similar to those of Fargesia, but differences arise in the arrangement of the florets. In Fargesia the racemes are held tightly within imbricating sheaths, which can extend well beyond the spikelets. Development within the sheaths forces them to emerge to one side and appear unilateral, with the pedicels tightly pressed against the rhachis. Those of Thamnocalamus tessellatus are more cylindrical, the spikelets not so constricted by the sheaths, and the pedicels are free to develop in a normal distichous fashion, Figure 1.

In addition, in Thamnocalamus tessellatus the pedicels are scabrous, the glumes of each spikelet are basally tight and contain no vestigial bud remnants, and the racemes are usually largely ebracteate. The usually single fertile florets also distinguish Thamnocalamus tessellatus from other Thamnocalamus and Fargesia species, but this character should be treated with caution as it can be a specific as well as a generic character.

Thamnocalamus tessellatus also hasvegetative characteristics that distinguish it, notably from Asian members of Thamnocalamus, (see Table 1). A close inspection of the branching reveals not the pattern seen in species such as Thamnocalamus crassinodus (T.P. Yi) Demoly, but instead the substantial reduction in sheathing seen in Fargesia, Yushania, and Borinda Stapleton, Figure 2.

The branches of Thamnocalamus tessellatus are subequal, arranged side by side through strong compression of the basal internodes of the central branch, accompanied by loss of some of the sheaths at the nodes, Fig. 2A, cf Thamnocalamus crassinodus, Fig. 2B. This allows lateral branch prophylls to be seen side by side without any intervening sheaths. These patterns were contrasted by Stapleton (1991; 1994: fig. 1; 1997: fig. 2), and also illustrated for Thamnocalamus tessellatus by Soderstrom and Ellis (1982: fig.1, fig. 4).

In addition to the synflorescence and branching, Thamnocalamus tessellatus also differs in minor details that are harder to quantify, including the more varied orientation of the foliage leaves, and the delicate appearance of its oral setae and their more varied orientation, Figure 3.

Thus in terms of vegetative macro-morphological characteristics important at the generic level, Thamnocalamus tessellatus is closer to Fargesia than to Thamnocalamus, but can be distinguished from both. In general appearance it resembles a coastal species of Pleioblastus Nakai from Japan, with rather loose clumps, erect culms with short branches bearing coarse, irregularly arranged foliage with persistent sheaths. This contrasts with the delicate foliage leaves, all oriented towards the light on pendulous branches seen in Himalayan speciesof Thamnocalamus and in Fargesia. This is likely to be associated with the more open ecological habitat in which Thamnocalamus tessellatus is found, rather than the darker forest understorey habitats of Asian Thamnocalamus and Fargesia species.

The synflorescence of Yushania alpina is practically indistinguishable from those of several Asian and American bamboos, including species of Arundinaria, Sarocalamus, and Yushania—an open panicle with nearly complete reduction in sheathing at points of branching so that it is essentially ebracteate. However, the sheaths are often reduced to small tough bracts, as well as the more delicate sheath remnants or tufts of hairs seen in similar genera. In addition the lateral spikelets are more often sessile or subsessile, without a long pedicel. However, these characters are relatively minor and quite variable.

Yushania alpina is more distinct vegetatively. Reaching heights of up to 20m in its natural habitat, the tall, very erect culms are potentially much larger than those of any Asian species of Yushania, which only reach a maximum height of about 7m. Culm nodes and branching also differ substantially from those of Asian species of Yushania, Figure 4.

Branches vary in size more than those of Asian Yushania species. The central branch is strongly dominant, and the first two lateral branches are also strong. The orientation of the branches is less erect than those of most species of Yushania, becoming nearly horizontal. Above the branches the internode is distinctly sulcate, much more prominently than is seen in Asian Yushania species, as a result of the development of strong branches. Moreover there is often a dense ring of short, partially developed aerial roots at nodes in the lower part of the culm, often extending into the mid-culm region as well. This character is only known in species of Chimonocalamus Hsueh & T.P. Yi, and the leptomorph-rhizomed Chimonobambusa Makino among the Asian temperate bamboos. The roots are not as sharp and thorn-like as those seen in Chimonocalamus and Chimonobambusa, but they can be very distinct and prominent. Nodes have a distinct infranode between the culm sheath attachment and the supranodal ridge, which is well developed, Figure 5.

In its natural habitat, the open stands have a widely spaced appearance closer to that of a species of Phyllostachys Siebold & Zucc., rather than the denser thickets of Asian Yushania species, because the rhizomes have consistently long necks, giving solitary culms rather than the denser clusters of pluricaespitose culms seen in Asian species of Yushania.

Branch structure and sheathing is difficult to distinguish from that of Yushania or Fargesia. Although the prophyll is usually 2-keeled, there is replication side by side of lateral branch initials without intervening sheaths. In this way it differs fundamentally from Chimonocalamus, which has only 3 branches and full sheathing.

Sufficient data is now available to test whether this classification would gain support from molecular phylogenetic evidence. These two African species were not clearly resolved with Asian representatives of any genera in any molecular studies. For example, in a comparison of ITS sequences (Guo et al. 2002), Thamnocalamus tessellatus did not resolve with the type species of Thamnocalamus, Thamnocalamus spathiflorus, and its position varied between topologies. In the nuclear ribosomal ITS analysis of Hodkinson et al. (2010), Yushania alpina did not group with other Yushania species or closely with any other taxon. Weak associations between Yushania alpina and Chimonocalamus species were found by Guo and Li (2004) and Triplett (2008), which is interesting as they share possession of aerial roots developed into thorn-like structures, although they differ in other ways. However, neither Yushania alpina nor Thamnocalamus tessellatus resolved with putative relatives in these or similar genera of temperate bamboos in the most comprehensive studies undertaken so far, using sequences from 8 regions of cpDNA in 146 species and 26 genera (Zeng et al. 2010), and 108 bamboos from 25 genera using plastid DNA and nuclear GBSSI gene sequences (Zhang et al. 2012).

The molecular data would suggest that their inclusion in Asian genera would render those genera polyphyletic. Because their monotypic status is considered likely they could not be supported as monophyletic groups themselves in a classification based solely on molecular phylogeny. However, Zeng et al. (2010) and Zhang et al. (2012) considered them both to represent distinct lineages, and it is not possible to place them in well supported meaningful monophyletic groups except the tribe Arundinarieae. Therefore while the molecular data would not allow the diagnosis of monophyletic genera for the African bamboos following a strict Hennigian cladistic analysis, neither their current placement in Thamnocalamus and Yushania, nor placement in any other existing genus receives any support either. Continuing to include these bamboos in Asian genera causes serious problems when describing or distinguishing between those genera.

Although woody bamboos are considered to have evolved originally in Gondwanaland rather than Eastern Asia (Hodkinson et al. 2010), these African representatives are nested within the northern temperate clade, the tribe Arundinarieae, with a largely Asian distribution. This is estimated to have diverged from other woody bamboos around 23 mya (Hodkinson et al. 2010), 29 mya (Bouchenak-Khelladi et al. 2010) or 37.5 mya (Christin et al. 2008), but to have radiated only ca. 9 mya (Bouchenak-Khelladi et al. 2010) 10 mya (Hodkinson et al. 2010), or 19 mya (Christin et al. 2008). Peng et al. (2013) after sequencing 95% of the Phyllostachys edulis genome found evidence of whole genome duplication 7–12 mya, supporting the more recent dates.

Collision of tectonic plates has been suggested as a likely cause of this rapid radiation (Stapleton et al. 2009, Hodkinson et al. 2010). African and Indian plates met the Eurasian plate around that time, allowing a biotic interchange and subsequent radiation and diversification of Gondwanan elements into a wealth of new habitats. However, the temperate ancestors of these two African bamboo genera seem to have diverged around the same time that temperate bamboos arrived in Eastern Asia. Inclusion of endemic temperate bamboos from S India, Sri Lanka and Madagascar in a molecular phylogeny is required before any conclusions can be drawn as to where bamboos from the northern temperate clade first evolved, but there seems no evidence for an African origin, and it seems more likely that temperate bamboos radiated from India to Asia, Africa, and N America.