Oocephala (S.B. Jones) H. Rob., 1999

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 : 82-83

Oocephala (S.B. Jones) H. Rob., 1999 Figures 17 A–B ; 18 A–F

Oocephala (S.B. Jones) H. Rob., Proc. Biol. Soc. Wash. 112(1): 230. 1999. Type species: Vernonia oocephala Baker

Vernonia subsect. Oocephalae S.B. Jones, Rhodora 83: 72. 1981.

Descriptions.

Low, much-branched shrubs to 1 m high, stems with L-shaped hairs on multiseptate stalks, cap-cells one-armed. Leaves alternate, sub-sessile, linear to elliptical, sometimes serrate. Inflorescences corymbiform cymes, with usually shortly pedunculate heads or with heads sessile in apical clusters of leaves. Involucre ovoid or cylindrical; bracts 20-40 in 4-7 gradate series, ovate to oblong, appressed; receptacle without pales. Florets ca. 10-15 in a head; corollas white or lavender, tubular to narrowly funnelform, throat as long as lobes, tips without hairs or with few short biseriate hairs; anther bases rounded, apical appendages glabrous, with thin-walled cells; style base with narrow ring; style branches with acicular sweeping hairs. Achenes weakly 8-ribbed, sericeous with many setulae, idioblasts numerous, raphids narrowly elongate; pappus biseriate, outer shorter and broader, inner setiform, subplumose, glabrous near base. Chromosome number unknown.

Pollen 7-8-porate, with pores scattered over the whole surface in lacunae that are usually not adjacent, lophate (Fig. 18 A–F ), minutely papillose on muri, nonperforated tectum restricted to muri, emicropunctate, baculae regularly spaced in single row under muri or lophae, baculae subtended by “rhizomate” structure that is as broad as the outer layer, and gives the muri or lophae a two-layed structure with small evenly spaced columellae separating the layers. The rhizomiform base of the muri is weakly attached to the footlayer thus causing muri to easily detach from the core of the grain. Lacunae of exine of pentagons mixed with hexagons. The structure of the bucky ball was a remarkable close approximation of the structure of the pollen. It was study of the toy ball that led to the conclusion that the pollen characteristically had seven or eight pores. Other pollen grains show a somewhat different pattern of pores, where pores occur in pairs, one each in a pair of adjacent lacunae (Fig. 18 B ). The polyporate, subspherically symmetrical, rhizomate form of pollen in Oocephala is shared in a somewhat less symmetrical form by Polydora , but as far is currently known, these Oocephala and Polydora grains, with their non-equatorial pores, are unique in the Asteraceae ( Robinson and Skvarla 2014).

Notable secondary metabolites: sesquiterpene glaucolides ( Bohlmann and Jakupovic 1990 as Vernonia staeheleinoides Harv.).

Figures

Figure 17. Photographs of Oocephala and Orbivestus: A-B Oocephala centauroides (Klatt) H. Rob. & Skvarla, note: egg-shaped head C-E Orbivestus cinerascens (Sch. Bip. in Schweinf.) H. Rob. See Appendix C for citation details.

Figure 18. Scanning electron micrographs of Oocephala staehelinoides (Harv.) H. Rob. & Skvarla. A Unacetylized grain showing three pores with caps intact, two pores in adjacent lacunae B-D Intact or nearly intact grains showing pores in both pentagonal and hexagonal lacunae B with pores in adjacent lacunae E Grain stripped of muri showing five pores and stubs of muri attachments F Segment of muri showing rhizomate structure and remnants of weak basal attachments to footlayer, (p) pore. A-F are from collection of Liebenberg 8843.