Lettowia H.Rob. & Skvarla, 2013

Robinson, Harold & Skvarla, John J., 2013, Lettowia, a new genus of Vernonieae from East Africa (Asteraceae), PhytoKeys 25, pp. 47-53 : 48-50

Lettowia H.Rob. & Skvarla gen. nov. Figs 1 , 2A, B

Type.

Vernonia nyassae Oliv.

Description.

Erect or decumbent perennial herbs from creeping rhizome or perennial root crown, all becoming erect, rosettiform, with erect pedunculate scapiform inflorescence; hirsute or pilose with long white hairs, hairs of stems, leaves and peduncles with cells uniseriate and with few short basal cells and long, acicular, rather stiff apical cell. Leaves alternate in loose basal rosette, mostly 2-4 cm long, petiole narrow, blade obovate, to 9 cm long and 1.5 cm wide, apically obtuse, cuneate into petiole at base, margins entire, slightly paler abaxially, pilose on margins and both surfaces, more densely pilose abaxially, few glandular dots adaxially, numerous dots abaxially. Scape mostly 5-11 cm long, densely and stiffly hirsute, sometimes with small bract near middle, bearing 1 terminal head. Heads broadly campanulate, up to 2 cm high, 1.5-1.8 cm broad. Involucre with ca. 15-20 persistent, mostly subequal ovate-lanceolate bracts in ca. 2 series, up to ca. 1.5 cm long, apices acute, without acumination, densely pilose outside with long simple hairs, with 3 longitudinal veins, margins narrowly scarious, sometimes reddish. Receptacle epaleaceous; florets ca. 40 in a head; corollas lavender, ca. 12 mm long, narrowly funnelform distally from slender basal tube, tube ca. 7 mm long, with stalked narrowly capitate glands outside, throat ca. 0.7 mm long, lobes linear, ca. 4.3 mm long, with glandular dots outside and numerous stiff uniseriate hairs distally; anther thecae ca. 3 mm long, with tapering bases, with short clavate tails, apical appendage oblong, glabrous, with tenuous cell walls; style base with narrow annular node; with acicular sweeping hairs restricted almost completely to branches; achenes weakly 5-costate, densely sericeous on and between ribs with long setulae, setulae slightly split at tips, glandular dots present near base, without evident idioblasts, raphids linear; carpopodium narrowly annuliform, with small quadrate cells; pappus of ca. 40 persistent barbellate bristles ca. 8 mm long, mostly of even width, tapering at extreme tips, with outer series of short narrowly lanceolate squamae. Chromosome number not known. Chemistry not known.

Pollen grains of Lettowia nyassae ( Fig. 2A, B ) ca. 55 µm in diam in fluid, ca. 45 µm dry, echinolophate, triporate, muri shortly echinate with 2-3 spicules on each mural segment, perforated tectum restricted to the muri. The lacunae are irregular in position and rather irregular in shape. The baculae are elongate, in a mostly single partially unaligned series under each murus, and they are firmly attached to the footlayer. In these features, the pollen is nearly like that of Vernoniastrum ( Fig. 2A, B ), and the relationship to that genus in the subtribe Erlangeinae is assumed. In direct comparison with the single species of Vernoniastrum for which SEM study of the pollen is available ( Fig. 2C-F ), a number of subtle differences can be seen. In Lettowia , the lacunae are larger in general and less numerous (ca. 25-30 in Lettowia versus 35-40 in Vernoniastrum ), the spicules on the muri are shorter and less numerous, and the baculae under the muri are mostly in a single row. In both genera there are lacunae that are elongate as if two lacunae are joined, but these do not seem to be aligned in positions where colpi might be located.

Etymology.

The genus is named for Colonel Paul von Lettow-Vorbeck, 1870-1964 ( Gunther 1956; Hoyt 1981; Lettow-Vorbeck 1920), who led the defense of German East Africa in WWI until the surrender of Germany, and was remembered fondly by the people of the former German colony on a return visit after WWII.

The genus contains the following single species.

Figures

Figure 1. Herbarium specimen of Lettowia nyassae (Oliv.) H. Rob. & Skvarla (A. Stolz 103, US).

Figure 2. A-F SEM of pollen. A-B Lettowia nyassae (Oliv.) H. Rob. & Skvarla (A. Stolz 103, US) A View with a pore B Surface lacking pores C-F Vernoniastrum nestor (S. Moore) H. Rob. (Burundi, Prov. Burundi, Gihofi (Mosso), 20 May 1980, Reekmans 9185, US) C View with a pore D Surface lacking pores E Closer view of lacuna with a pore F Closer view of surface without pores showing extra rows of baculae.