Studies in the Gramineae XXV

Abstract

Due to a lack of sufficient material Hubbard (Fl. Trop. Afr. Io: 123 (I937)) stated that his classification of the African species of Pentaschistis must be regarded as purely provisional. In his key P. pictigluma and P. mannii are separated on the size of the floral parts, even though the measurements show a small degree of overlap. At that time P. pictigluma was only known from Ethiopia, while P. mannii, which has somewhat larger spikelets, was restricted to the Cameroun Mountains, with a doubtful record from Mount Meru in Tanzania. Since then additional specimens from Uganda (Mt. Elgon and Mt. Moruongole) and Kenya (Aberdare Mtns.) have been tentatively named as P. mannii. These East African specimens differ in having slightly larger spikelets and longer and less adpressed hairs on the lemmas. Specimens from the Sudan Republic (Jebel Marra) had been named as P. pictigluma. Sufficient material is now available from Ethiopia and the Cameroun Mountain for the status of the two species to be considered more critically. The average of three measurements taken from dry herbarium material were recorded for the length of lower and upper glume, body, lateral bristle, awn column and limb of the lemma. Histograms (Fig. I, p. 42) were then constructed using awn and column length, the chief characters used by Hubbard to separate the two species. The histograms show that the dimensions of the Ethiopian and West African material overlap slightly, with the East African and Jebel Marra specimens occupying an intermediate position. Scatter diagrams using various combinations of the characters measured, failed to show any disjunction between the two species; the Ethiopian plants were shown to be generally smaller than those from the Cameroun Mountain, with Jebel Marra intermediate between the two, as might be expected from its geographical position. One of the scatter diagrams is illustrated (Fig. 2, p. 43)Although P. mannii cannot be considered as specifically separable from P. pictigluma the East African specimens might possibly deserve subspecific status, but there is still insufficient material available to make such a decision.