Longhi-Wagner, H.M. & Cope, T.A. 2014. The genus Ctenium (Poaceae: Chloridoideae: Chlorideae) in Africa. Kew Bulletin 69: 9541. DOI https://doi.org/10.1007/s12225-014-9541-x
Nees von Esenbeck (1841) described Ctenium concinnum based on a collection by Drège, as having “valvulae flosculorum inferiores …, dorso et margine longe ciliate ciliis erectis” and this can clearly be seen in the type material deposited at B and P Herbaria (Fig. 2C). The presence of a ring of long spreading hairs at the base of the spike, at the junction with the peduncle, is also typical of C. concinnum (Fig. 2K).
Chiovenda (1897) described Ctenium nubicum var. somalense, from specimens Riva 180 and 525, as having “flosculus summus neuter undique breviter pubescens”. However, the first and second lemmas of specimens Riva 180 and 525 are lanceolate, acute to subacute, covered all over by long, silky hairs, not just on the keel and margins (Fig. 3D).
Pilger (1924) described Ctenium concinnum var. indutum and var. minus, differing by the shape and indument of the lemmas. The first lemma of the holotype of var. indutum (Fig. 3J) has a similar shape to that of the type of var. minus (Fig. 3H) but is slightly longer, with denser and slightly longer cilia on the keels and margins.
Another characteristic that can be used to differentiate between Ctenium concinnum and C. newtonii is the length of the first and second lemmas, which is generally greater in C. concinnum. In variants of C. concinnum in which the length of the first and second lemmas is similar to that more commonly found in C. newtonii, it was observed that the presence of a dense tuft of long hairs (3 – 4 mm) at the apex of the leaf sheath is constant, and the sheaths usually become fibrous with age forming a single dense mass of fibres at the base of the plant. In C. newtonii the sheaths are generally glabrous at the apex, less commonly with sparse hairs (1 – 3 mm), and do not become fibrous with age.
Among the material collected in the Chimanimani Mountains (Zimbabwe), we found the greatest number of plants intermediate between typical Ctenium concinnum var. concinnum and var. minus. This would be a suitable area for further studies of the C. concinnum complex.
Clayton (1963) treated Ctenium concinnum var. minus as C. concinnum and included C. concinnum var. indutum in its synonymy. Later, Clayton et al. (1974) accepted the name C. somalense, including C. concinnum var. minus and C. minus in its synonymy. In the same reference Clayton noted that C. concinnum is “a southern African species integrating with C. somalense. The East African specimens are mostly of an intermediate nature with a slightly fibrous base”. He also emphasised that “Ctenium somalense is replaced in the southern half of the continent by C. concinnum, with which it has often been confused by East African authors”. Apart from the differences in dimensions, form and indumentum of the first lemma, Clayton (1963) mentioned that the basal leaf sheaths of plants of C. concinnum usually become “chaffy like wood-shavings” (Fig. 2F), while in C. minus they usually become fibrous (Fig. 2A), this character being used in the analytical key presented.
Cope (1999) treated Ctenium concinnum and C. somalense for Flora Zambesiaca using the same criteria as Clayton et al. (1974), and mentioned that “specimens from Uganda, Kenya and Tanzania tend to be somewhat intermediate between this species [C. concinnum] and C. somalense”. When considered one species only the oldest name (thus to be accepted here) is C. concinnum.
The type material of both Ctenium concinnum and of C. concinnum var. minus seem to represent the extremes of a continuous morphological variation with intermediates, some of which resemble the type material of C. concinnum var. indutum (e.g. Willd 2900; Fig. 4A, B). Specimens resembling the type material of C. concinnum and C. concinnum var. indutum predominate in southern Africa; they are mostly plants with a chaffy base (e.g. Loveridge 1666, Fig. 4C), but others have a fibrous base and these can also be found in Somalia. Specimens from tropical East Africa, Madagascar and Mascarene Islands have spikelets similar to those of C. concinnum var. minus; collections from the east generally have a fibrous base (e.g. Magogo & Glover 279; Fig. 2A), but those from Madagascar do not (e.g. Hildebrandt 4000; Fig. 3F). However, in the intermediate area they intergrade, as observed by Clayton et al. (1974), and are morphologically intermediate, e.g. Germain 6524 with a fibrous base and spikelet dimensions as in var. minus, a lanceolate first lemma, as in C. concinnum, and an indumentum intermediate between the two variants (Fig. 4F). Specimen Corby 782 (Fig. 4G) also has a fibrous base but the first lemma is like that of C. concinnum. Specimen Johnston 1225, from Central Africa, is another example without a fibrous base, but with spikelet shape and length similar to that of C. concinnum var. minus, the indumentum of the first and second lemmas being intermediate (Fig. 4N). These variants can probably be found within the same population because duplicates of the collections found in other herbaria had variations in the shape and type of indumentum of the first and second lemmas, making it difficult to decide to which taxon they belong. These variations in shape, dimensions and indumentum of the lemmas are illustrated in Fig. 4.
Clayton et al. (1974) mentioned that Ctenium somalense (here referred to C. concinnum) tends to intergrade with C. newtonii Hack. in tropical East Africa, and that these C. concinnum specimens can only be recognised as such by the presence of a typical ring of long hairs at the base of the spike (e.g. Greenway 10767; Fig. 2K). According to our data, this intermediate morphology is uncommon, but it was also observed in specimens from Central Africa (Congo and Burundi). In a smaller number of specimens some flowering culms have a ring of long hairs at the base of the spike, while others are bearded with 0.5 – 0.8 mm long adpressed hairs (Germain 6168; Fig. 4H). Other examples of intermediate morphology are the specimens Shanty 723, Fay 3194, Lewalle 2823 and Symoens 10082. The variation in the presence/absence of a ring of hairs at the base of the spike was also observed in specimens collected in Madagascar, including one isotype of C. concinnum var. minus (Hildebrandt 4000) deposited at K. However, these specimens from Madagascar have a cuspidate first lemma pilose between the nerves, as in var. minus, and so they are here determined as C. concinnum.
Ctenium concinnum Nees is recognised mostly by the presence of a dense ring of long hairs (1 – 2.5 mm) at the base of the spike, at the junction with the peduncle. The first and second lemmas are lanceolate and densely silky-pilose all over in those specimens similar to the type material of C. concinnum and of C. somalense, whereas the first lemma is elliptic-lanceolate and cuspidate, and sparsely pilose between the nerves, in those specimens similar to the type material of C. concinnum var. minus. However, many intermediate specimens were observed.Apart from the presence of a ring of hairs at the base of the spike — occasionally absent in some culms on one specimen — Ctenium concinnum always has spikelets with 5 florets.
Gramineae, W. D. Clayton, S. M. Phillips & S. A. Renvoize. Flora of Tropical East Africa. 1974
Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592
Gramineae, T. Cope. Flora Zambesiaca 10:2. 1999
