Vernonella Sond., 1850

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 : 95-96

Vernonella Sond., 1850 Figures 13 D ; 25 A–I

Vernonella Sond., Linnaea 23: 62. 1850. - Type: Vernonella africana Sond.

Resources.

Species reviewed by Smith (1971) and Robinson and Skvarla (2010a).

Descriptions.

Annual or perennial herbs, with leaves rosulate or on leafy stems, basal rosettes often withered at anthesis, bases of plants erect, with or without a dense basal cloak of hairs. Hairs simple or lacking on stems. Inflorescences monocephalic, laxly cymose or densely corymbiform, with short to very elongate peduncles. Heads broadly campanulate; involucres 3-6-seriate, bracts broadly to narrowly oblong, gradate with basal bracts often more lanceolate, tips of inner bracts often obtuse to rounded or apiculate, distally and marginally rather scarious, often purplish. Florets 10-50 or more in a head; corollas purple, with long slender basal tube, throat short, not noticeably broadened at base, lobes linear, usually contorted with age, bearing glands, simple hairs, or L-shaped to T-shaped hairs; anther thecae calcarate and blunt at base, without tails; apical appendage oblong-ovate, with thin cell walls; style base with annulus of thickened, quadrate cells; sweeping hairs slender with sharp, narrow tips. Achenes with ca. 10 ribs, setulose on ribs, setulae with paired cells separated in distal third or less, with numerous idioblasts on surfaces between ribs; raphids in achene wall narrowly elongate. Chromosome number n = 9 ( Jones 1982).

Pollen ca. 30-40 μm in diameter when dry, tricolporate with short or truncated colpi, sharply echinate with elongate spines, sublophate with large irregularly shaped lacunae, perforated tectum continuous in lacunae (Fig. 25 A–C ).

Notable secondary metabolites include sesquiterpene lactones (elemanolides and eudesmanolides).

The genus Vernonella is most notable for its often solitary heads, simple vegetative hairs, the comparatively limited differentiation of the involucral bracts, unexpanded corolla throats, and the comparatively small sublophate rather than lophate pollen with uniquely truncated colpi. On the basis of the examination of the type species, the detailed studies of Smith (1971), and reviews of literature, eleven species are recognized in the genus. The genus is restricted to Africa and is distributed from Cameroon and Sudan in the north southward to Natal in South Africa.

Figures

Figure 13. Illustrations Hilliardiella, Linzia, Parapolydora, and Vernonella: A Hilliardiella capensis (Houtt.) H. Rob., Skvarla & V. A. Funk B Linzia glabra Steetz in Peters, note: characteristic teeth on involucral bracts C Parapolydora gerrardii (Harv.) H. Rob D Vernonella africana Sond. See Appendix C for citation details.

Figure 25. Scanning electron micrographs of Vernonella and Vernoniastrum. A-C Scanning electron micrographs of acetolyzed sublophate-echinolophate pollen of Vernonella africana Sond. A Polar view B Equatorial view C Oblique polar view. A-C from Wood 753. D-I Scanning electron micrographs of acetolyzed echinolophate pollen of Vernoniastrum nestor (S. Moore) H. Rob., showing diversity of lacunae and lophae. D-H Oblique and near polar views showing apertures in markedly long lacunae with irregular lophae H Lateral view with apertures (arrows) occupying long lacunar spaces I Enlarged section of surface showing columellae in irregular rows under muri). D-I from Reekmans 9185.