Psathura

Taylor, Charlotte M., 2020, Overview of Psychotria in Madagascar (Rubiaceae, Psychotrieae), and of Bremekamp’s foundational study of this group, Candollea 75 (1), pp. 51-70 : 60

Psathura

Bremekamp’s Psathura

BREMEKAMP (1963) characterized and expanded the classical genus Psathura , which he diagnosed by ovary and pyrene characters, but his circumscription and characterization of this genus are also problematic morphologically. He diagnosed Psathura by its 3- to 5-locular ovaries, and fruits with 3 to 5 pyrenes that are triangular in cross-section and have two plane adaxial faces ( Fig. 4F–I ). He also informally characterized Psathura by endosperm that is not ruminated. Bremekamp’s Psathura included four species from Madagascar that are heterogeneous in other morphological features, plus four other species from Mauritius and Reunion. As noted above, the presence and pattern of endosperm rumination is variable across Psychotria without evident systematic pattern. The multilocular ovaries and triangular pyrene shape are not separate characters, because pyrene form is constrained by the packing of several pyrenes into a subglobose structure. Abaxially the pyrenes of his Psathura species vary markedly, from smooth to deeply longitudinally ridged, so this characterization was not accurate.

This leaves the multilocular ovary as the only diagnostic feature for Psathura , and it is a morphological character of interest in Rubiaceae but is problematic as a diagnostic character of a genus. Number of ovary locules and pyrenes is variable in many Rubiaceae tribes and genera ( ROBBRECHT, 1988) and within some species ( STEYERMARK, 1972). Psychotria has mostly 2-locular ovaries, but this condition does vary. For example, several African species of Psychotria were separated as Camptopus Hook. f. based in part on their 3- to 4-locular ovaries, but RAZAFIMANDIMBISON et al. (2014) found these species nested within Psychotria . Number of ovary locules was noted by BREMEKAMP (1963: 175) himself to vary within some Psathura species. The separation of Psathura from Psychotria based on 3 vs. 2 ovary locules is at best arbitrary, and this difference is now blurred by a newly discovered species with both 2- and 3-locular ovaries on the same plant (TAYLOR, in press). Psathura was not mentioned by SCHATZ (2001), but was recognized by other authors ( PIESSCHAERT, 2001; DAVIS et al., 2007).

Bremekamp’s Psathura analyzed with molecular data ANDERSSON (2002) did not find enough information to evaluate Psathura , and considered it a name of uncertain application. RAZAFIMANDIMBISON et al. (2014) included five Psathura species in their molecular analysis, two from Madagascar and three from the Mascarenes, and found them all deeply nested on a clade of Psychotria . Razafimandimbison et al. found two groups within their Psathura species, with the Mascarene species grouped together and the Madagascar species grouped with several species of Bremekamp’s Psychotria . They did not analyze the systematics of multilocular ovaries, but mapping this feature on their cladogram now finds some of the multilocular Psathura species separated from the multilocular Camptopus species and some of them from each other, and this feature to be homoplasious.

Figures

Fig. 4. – Some morphological features of Psychotria L. in Madagascar. A–B. Apomuria, Psychotria biloba (Bremek.) A.P. Davis & Govaerts: A. Fruiting branch; B. Cross-section of seed (removed from pyrene). C–D. Apomuria, Psychotria punctata Vatke: C. Fruit; D. Cross-section of seed. E. Psychotria kirkii Hiern, cross-section of seed. F–G. Psathura, Psychotria borbonica (J.F. Gmel.) Razafim. & B. Bremer: F. Fruit; G. Cross-section of fruit, with four pyrenes. H–I. Psathura, Psychotria batopedina (Verdc.) Razafim. & B. Bremer: H. Fruit; I. Cross-section of fruit, with five pyrenes. J. Unusual stipules in Malagasy Psychotria L. (TAYLOR, in press). K–N. Trigonopyren, Psychotria tsiandroi Razafim. & B. Bremer.: K. Node near stem apex with developed stipule, unbroken and with glandular projections; L. Node below the node shown in K, with aging stipule that is falling off in fragments; M. Node in lower part of stem, with old stipule that has fallen off except for persistent basal part of sheath; N. Cross-section of pyrene. O–P. Trigonopyren, Psychotria bealanensis Razafim. & B. Bremer: O. Fruit; P. Cross-section of fruit, with two pyrenes.