Achyranthemum N. G. Bergh 2019
Creators: name: Bergh, N. G.
name: Manning, J. C.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Asterales
Asteraceae
Achyranthemum

description: 3.1. Characters of Achyranthemum
Habit: Species of Achyranthemum are usually sparsely branched, but sometimes bushy, softly woody subshrubs with erect stems, rarely prostrate and clump-forming (Figs. 3C, 4A, 8A). The branches are woody below, with the leaves clustered towards the branch apices. The synflorescences are borne at the tips of the flowering shoots, and the following year’ s growth commences from below the synflorescence.
Foliage: The leaves are alternate or rarely alternate-decussate, and usually imbricate, generally firm-textured to rigid, linear-subulate to narrowly oblanceolate, sessile and sometimes decurrent on the stem, basally appressed to erect, and frequently apically recurved or with hooked apices. The lamina is either flat, rolled around the adaxial surface or weakly to strongly conduplicate. Leaf length ranges from ± 8 mm to over 30 mm, rarely up to 65 mm, and leaf width varies from ±0.8 up to 5 mm. Margins are somewhat involute. The midrib and sometimes lateral veins are prominent and visible on the abaxial surface if the tomentum is not too thick, or on drying. All species have leaves with an indumentum of extremely long, slender, antrorse hairs. In most species, these hairs cohere to form a reticulating sheath-like covering to the leaf, this covering being especially thick and well-developed in A. paniculatum, A. mucronatum and on the abaxial leaf surface in A. recurvatum (Figs. 3A, 4C & 5D), and so obscuring the leaf surface. In the first two species, the bases of the hairs form a finer arachnoid layer closer to the leaf surface. Achyranthemum recurvatum (Fig. 5D) lacks this arachnoid layer but the hairs in this species cohere strongly, forming very thick ropy silvery strands that project off the leaf margin like soft curling spines. In A. argenteum (Fig. 6B) and A. af fi ne (Fig. 7B), the reticulating sheath is very thin and fine, closely following the contours of the leaf surface so that the shapes of the leaf veins are discernable.
In A. sordescens, the hairs cohere basally very strongly to the epidermis, forming a thin but very strong layer above which the long free ends of the hairs are tangled but not cohering, forming a loose tangled villous layer (Fig. 8D). Achyranthemum striatum is the only species that completely lacks the sheathing hair-layer. In this species (Fig. 9B, D) the long antrorse hairs are free and more-or-less straight, not tangled or cohering, and usually much sparser than in the aforementioned taxa, so that the glabrous leaf surface is visible beneath the hairs.
Syn fl orescence: The arrangement of multiple capitula at the end of a single flowering shoot is termed a synflorescence. One species, A. recurvatum, has strictly solitary capitula, while the remainder have corymbiform synflorescences. Rarely, one of these corymbiform species may have a stem with a solitary capitulum, but then usually on the same plant synflorescences can be found comprising at least 2 and up to12, or rarely up to 40, capitula. Capitula or synflorescences are borne at the branch apices on short felted flowering stalks, on peduncles that are always woolly or variously pubescent, and are between 2 and 60 mm long. The peduncles usually bear one or two widely spaced bracteoles that are similar to the involucral bracts in structure.
Capitula: The capitula are globose or rarely cylindrical in shape, varying in size between 7 and 18 × 4 and 18 mm, with 40–120 involucral bracts. The individual involucral bracts comprise a thickened, cartilaginous basal stereome and a thinner, papery apical lamina (Fig. 2C). The lamina also flanks the stereome marginally. The stereome is unfenestrated, strongly convex or curved basally, often coloured plum-purple apically, is usually villous or bears a villous patch on the abaxial side, and is glabrous adaxially. The size of the stereome relative to the lamina increases from the outer to the inner bracts.The outer and middle bracts are large and lanceolate, longer than the flowers and ± squarrose, while the inner bracts are generally narrower with the stereome comprising most of their length, topped with a small obtuse lamina, and ±as long as the florets. These inner bracts are hidden by the outer bracts and held erect to form a palisade or wall surrounding and protecting the florets. The outer bracts are larger and showy, the recurved laminas often forming a ‘landing platform’ for pollinators. All involucral bract laminas are smooth and shiny, with colours ranging from bright white to cream to pale yellow or dark yellow. In several species, the laminas are flushed pink when immature, and in two species the pink colour persists to maturity. Bract colour is another important character for species discrimination. The involucral bracts tend to close up when the heads are placed in a moist environment (e.g. inside a collecting bag) and open again on drying.
Receptacles: Receptacles are epaleate in all species of Achyranthemum, being tubercled or honeycombed and flat.
Florets: Only hermaphrodite florets are present in the capitula of Achyranthemum, with the number of florets in a capitulum varying from ±30 (in A.sordescens and in small-headed forms of A.paniculatum) to over 100 (in A. argenteum and in large-headed forms of A. paniculatum). The corolla is obconic to funnel-shaped, widening apically (Fig. 2F). Corolla lobes are small, deltoid and recurved at maturity, and bear globose trichomes abaxially. The florets can be as small as 3.5 mm long (in A. mucronatum) and up to 7 mm long (in A. striatum and A. sordescens).
Anthers: The anthers are ecalcarate and minutely tailed; the endothecial tissue is polarised, as in most other Gnaphalieae, and the apical anther appendages are mucronate, caudiculate or acuminate.
Cypselae: The cypselae are small, 0.8–3.0 mm long, ovoid or cylindrical, generally reddish-brown at maturity, and are sparsely covered with hemispherical myxogenic twin hairs (Fig. 2D), that according to Hilliard and Burtt (1981b) lack a basal swelling cushion. When wetted, these produce copious amounts of clear mucilage, making the cypselae extremely sticky.
Pappus: The pappus comprises a single series of bristles (Fig. 2A, B) that are fused at the base into a smooth ring. The bristles are basally scabrid to barbellate, generally with larger barbs towards the apex, where the cells are larger, acute and generally more tightly appressed.
Flowering time: All members of Achyranthemum have their main flowering time in the austral spring, September to December, but it is not uncommon to find flowering specimens in the winter months.
Geographic distribution: The genus is almost restricted to the Core CFR (sensu Manning and Goldblatt, 2012), with one species extending further east to Grahamstown. The centre of diversity is in the Algoa Bay area around Port Elizabeth, where five of the species are endemic or nearly endemic, mostly in coastal plain or true coastal dune habitats, and only one species, A. paniculatum, has colonised the Cape Fold mountains.
description: Published as part of Bergh, N. G. & Manning, J. C., 2019, Achyranthemum N. G. Bergh, a new genus segregated from Syncarpha DC. (Asteraceae, Gnaphalieae) *, pp. 434-456 in South African Journal of Botany 125 on pages 439-440, DOI: 10.1016/j.sajb.2019.08.015, http://zenodo.org/record/10496693