Distephanus Cass., 1817

Robinson, Harold, Skvarla, John J. & Funk, Vicki A., 2016, Vernonieae (Asteraceae) of southern Africa: A generic disposition of the species and a study of their pollen, PhytoKeys 60, pp. 49-126 : 61-62

Distephanus Cass., 1817 Figures 4 G–I ; 6 A–H

Distephanus Cass. Bull. Soc. Philom. Paris 1817: 151. 1817.

Gongrothamnus Steetz in Peters, Reise Mossamb., Bot.: 336. 1864. - Type: Gongrothamnus divaricatus Steetz in Peters

Newtonia O. Hoffm. in Engler & Prantl, Natürl. Pflanzenfam. 4(5): 285. 1892, nom. illeg., non Baill. 1888. - Type: Newtonia angolensis O. Hoffm.

Antunesia O. Hoffm., Bolet. Soc. Brot. 10" 178. 1893 ( “1892”), nom. nov. for Newtonia .

Resources.

For discussion and numerous transfers of species see treatment by Robinson and Kahn (1986). For a recent treatment of the genus in southern Africa see Swelankomo and Manning (2014).

Descriptions.

Shrubs or vines; hairs arachnoid, contorted or asymmetrically T-shaped. Leaves alternate; petioles short; blades ovate to rounded, often with truncate to subcordate bases, less often narrow with cuneate bases, margins usually entire or subentire, venation usually with stronger more ascending basal pair or strongly triplinervate, less often irregularly pinnate. Inflorescences terminal on stems or branches, with single heads or usually branching, corymbiform with minute bracts or thyrsoid with foliose bracts; peduncles usually short. Heads with campanulate involucres; bracts 21 –24(– 75) in 4 –6(– 7) gradate series, without appendaged tips; receptacles epaleaceous. Florets 10 –16(– 75) in a head; corollas usually yellow, purplish in a few continental African species; anther thecae with distinct broad often sclerified basal appendages; endothecial cells with simple, broad, non-contiguous, sclerified shields; apical appendages without glands; style base with large abruptly distinct node; style branches with obtuse sweeping hairs. Achenes cylindrical to prismatic, sometimes subtriquetrous or quadrangular, with 5-12 ribs, usually 10, setulae or glands present or absent, raphids elongate; carpopodium turbinate; pappus of many capillary bristles, outer series of squamellae. Chromosome numbers n = 9, 10, 15 ( Jones 1982, Gill and Omoigui 1992).

Pollen: 30-36 μm in diameter (dry); tricolporate, sublophate to lophate; lophate forms with muri projecting as spurs into colpus, with echinate or with nearly psilate ridges; tectum continuous in intercolpi and at poles, or in pockets surrounded by ridges, with distinct perforations; with columellae under spines or with muri granular inside, without distinct baculae (Figs 4 G–I ).

Notable secondary metabolites: sesquiterenes, elemanolides (Bohlmann and Jakupovic, as Gongrothamnus aurantiaca N.E. Br.), guaianolide (as Gongrothamnus sublutea Elliot., guaianolides ( Bohlmann and Jakupovic 1990, as Vernonia anisochaetoides Sond., glaucolides/hirsutanolides ( Bohlmann and Jakupovic 1990, as Vernonia angulifolia DC., Vernonia tufrnellae S. Moore).

Figures

Figure 4. Scanning electron micrographs of acetolyzed pollen of echinolophate Bothriocline and Cyanthillium and sublophate-lophate Distephanus. A-C Bothriocline schimperi Oliv. & Hiern ex Benth. A Equatorial view, note incipient colpus of 3 connected lacunae centered on pore B Near polar view C Fractured grain D-F Cyanthillium cinereum (L.) H. Rob. D Equatorial view E Lateral view with apertures on sides F Lateral view G-I Distephanus angustifolia (DC.) H Rob. & B. Kahn. G Polar view H Equatorial view I Lateral view. (A-C, F. Meyer 8159; D-F, Evans 344; G-I, Sidley 2211).

Figure 6. Photographs of Distephanus: A-F Distephanus divaricatus (Steetz) H. Rob. & B. Kahn; G-H Distephanus anisochaetoides (Sond.) H. Rob. & B. Kahn. Note the variable flower color in Distephanus divaricatus. Note: trinervate veination, lack of lavender corollas and presence of yellow and orange. See Appendix C for citation details.