Achyranthemum mucronatum (Berg.) N.G.Bergh, 2019

Bergh, N. G. & Manning, J. C., 2019, Achyranthemum N. G. Bergh, a new genus segregated from Syncarpha DC. (Asteraceae, Gnaphalieae) *, South African Journal of Botany 125, pp. 434-456 : 444-446

4.2. Achyranthemum mucronatum (Berg.) N.G.Bergh , comb. nov.

Gnaphalium mucronatum Berg., Descr. Pl. Cap. : 269 (1767). Xeranthemum tenuifolium N.L.Burm., Prod. Fl. Cap. : 26 (1768), nom. illeg. super fl. Helichrysum mucronatum (Berg.) Less., Syn. Gen. Compos. : 295 (1832). Helichrysum mucronatum var. citreum Harv. in Fl. Cap. 3: 226 (1865), nom. illeg. super fl. Syncarpha mucronata (Berg.) B.Nord. in Comp. Newsl. 39: 54 (2003).

Type: without locality or date,? Auge s.n. [G-PREL G00804045, lecto.– digital image!, specimen illustrated in Burman, Rar. Afr. Pl.: 179, t. 66, f. 3, designated by Hilliard & Burtt: 244 (1981a)]

Helichrysum chlorochrysum DC., Prodr. 6: 179 (1838). Syncarpha chlorochrysum (DC.) B.Nord. in Comp. Newsl. 39: 54 (2003). Type: South Africa, Western Cape, ‘Cap. Zwellendam’, Ecklon s.n. (G-DC G00470387 , holo.– digital image!).

Small, erect or sprawling, sparsely ramified shrublet branching near the base, usually 0.2–0.7 m but up to 1.5 m high, stems woody at base. Leaves imbricate, sessile, appressed or erect with apices weakly spreading to recurved; linear to linear-lanceolate to broadly lanceolate, varying greatly in width, bases decurrent, free portion 10–25 × 1.0–12.0 mm, pungent, apical mucro ± 1.2 mm long, apically concave, five parallel veins visible in broad-leaved specimens, both surfaces with very long (2–3 mm or longer) silvery-white arachnoid hairs that cohere to form a a thick, longitudinally oriented irregularly reticulating lattice-like sheath, indumentum less developed, thinner and more compact on the concave adaxial surface, strongly developed abaxially particularly on the apical portion of leaf. Capitula terminal in groups of (1–)2 to 12 (–30) in a compact pseudo-corymb, shortly cylindrical, 7–13 mm long by 10–15 mm wide, sessile when in bud but pedunculate on maturity; peduncles 10–25 mm long, densely woolly with a thick layer of very fine interwoven white hairs; involucral bracts ±50–120, in ±6 series, erect; lamina when mature coloured pale to dark yellow, when immature very pale yellow often tinged pink; outermost ovate, entire bract 4–7 × 2–3 mm, middle lanceolate, 5–9 × 3 mm, innermost linear with acute apex, smaller than middle and outer, 4–5 × 0.5–1.0 mm. Florets ±40–90(–100), corolla tube 0.5 mm diam., gradually expanding from base to apex, pale yellow, 3.5–5.5 mm long including lobes; anther apex rounded with an acuminate central caudicle. Cypselae cylindrical, 0.8–1.0 × 0.6 mm, pale brown. Pappus bristles united at the extreme base, shorter than fused length of corolla tube, shaft finely barbellate, barb cells becoming stouter and more tightly appressed at apex. Flowering time: The main flowering period is from October to December but buds can be found from June and plants can be seen in late stages of flower until April ( Fig. 4 ).

Distribution and ecology: Confined to the Agulhas Coastal Plain in the Bredasdorp region and probably specialised to the calcrete soils particular to this area, from near sea level to about 330 m elevation. The westernmost collection is ‘Kleinmond Honingklip Pakskuur’ (Van der Walt 19 [NGB]) but since it is mentioned as a cut-flower collection, this might not be accurate, and Pearly Beach is the westernmost verified locality. The easternmost collection locality is Stilbaai.

Diagnosis: A. mucronatum is a sub-shrub with grey-green, silvery leaves and yellow heads, occurring only in the Agulhas plain area. It is very variable in size of the leaves, capitula and synflorescences, but always has ±yellow involucral bracts. This distinguishes it from the vegetatively similar A. paniculatum which has white involucral bracts and occurs mainly inland on sandstone substrates. On the south side of the Potberg in the De Hoop Reserve the two species co-occur, (e.g. Morley 133 [PRE], a mixed collection of A. paniculatum and A. mucronatum ), but can always be distinguished by bract colour.

Conservation status: Syncarpha chlorochrysum , which forms a large part of this revised concept of Achyranthemum mucronatum , is listed as near-threatened (www.redlist.sanbi.org accessed August 2018), having an extent of occurrence smaller than 2300 km 2 within areas experiencing coastal development and alien plant infestations. While the current concept of A.mucronatum will result in an increased number of specimens and localities, the overall extent of the range does not change significantly, and a revised conservation assessment is required.

Taxonomic note: The taxonomy of A. paniculatum and A. mucronatum as been very confused, and several taxa have been described to accommodate the morphological variation evident in the species. The two species are vegetatively similar, with linear to linear-lanceolate or ovate-lanceolate leaves covered by an identical sheathing reticulating indumentum of stout silvery hairs. Achyranthemum paniculatum has white capitula, whereas the type specimen and protologue of A. mucronatum indicates that it has pale to dark yellow capitula. The colour differences are always distinguishable in specimens with mature heads, but immature heads of the yellow-coloured taxa are often paler. The yellow-headed specimens are restricted to the calcrete-rich substrates of the Agulhas plain. Similarly to A. paniculatum , A. mucronatum exhibits a range of variation, from forms with slender and terete leaves (currently called Syncarpha mucronata ) to those with broad and flat leaves (called Syncarpha chlorochrysum ). Specimens also differ in capitulum size and arrangement, with specimens corresponding to S. mucronata having smaller capitula clustered in smaller, more lax synflorescences while those corresponding to S. chlorochrysum have larger capitula in bigger clusters. These form a striking terminal corymbose synflorescence, the appearance of which is sometimes enhanced by a shortening of the leaves below. Specimens representing the extremes of these two conditions are strikingly distinct and if there were no intermediate forms, would undoubtedly be recognised as separate species, as has been done until the present. However, leaf width in yellow-headed specimens is highly variable, possibly enhanced by different degrees of involution. The same holds for capitulum size and arrangement, and large values in one character are not neccessarily associated with large values in the others (e.g. many specimens have broad,short leaves but small capitula clustered in lax, few-headed synflorescences, while several narrow-leaved specimens have large capitula). Examination of all specimens in BOL, NBG, PRE and SAM did not uncover characters which can separate the specimens into two distinct taxa. However, the geographic variation in A. mucronatum these characters is worth noting. Almost all of the small, terete-leaved and small-headed specimens occur on the Elim coastal plain south of the Bredasdorp mountain range, from Baardskeerdersbos in the west to Die Poort in the east, while the core area for the broad-leaved, large many-headed specimens occurs in the Potberg limestones and eastwards to Vermaaklikheid.

While S. chlorochrysum is generally consistently applied to specimens with yellow heads and and broad leaves, herbarium workers have frequently missed the fact that the type of S. mucronatum has yellow bracts, and folders under this name generally house slender, narrow-leaved specimens with white bracts, derived from De Candolle’ s H. mucronatum var. niveum .

Examination of all available specimens of A. paniculatum and A. mucronatum indicated that while two groups could almost always be distinguished based on bract colour (white vs. yellow) and distribution/habitat (inland sandstone slopes vs. coastal calcretes), within these two groups the criteria of leaf shape and size, and capitulum size and number, failed to differentiate additional taxa. Thus Achyranthemum mucronatum is morphologically very similar to A. paniculatum and is similarly variable, particularly in leaf width and capitulum size, as well as the number of capitula in a synflorescence. Leaves can vary from being almost terete and less than 1 mm wide, to over 9 mm wide, while mature capitula vary from being less than 8 mm to over 12 mm in length, and from being solitary to clustered in corymbiform synflorescences comprising over 30 individual capitula.

History: Gnaphalium mucronatum was described by Bergius in 1767. The lectotype for this name ( Hilliard and Burtt, 1981a) is a specimen illustrated in Burmann (1739) under the polynomial ‘ Xeranthemum frutescens , foliis linearibus angustissimum, capitulis sulphureis ’. The description ‘sulphureis’ (sulphur-yellow) matches the pale yellow capitula of one of the associated specimens (Ecklon 959 [G-DC G00470521]) while two others (G00470547 and G00470546) have white heads. All these specimens have slender leaves and small capitula in few-headed synflorescences. A note by Olive Hilliard on the specimens in G-DC indicates that the two white-headed specimens are rather associated with ‘var. niveum ’. Hilliard is here referring to Candolle's (1838) publication in which he segregated white-flowered plants of A. paniculatum under this trivial epithet, which he identified as being synonymous with Anaxeton racemosum Schrank. In the same publication, Candolle (1838) described a new species, Helichrysum chlorochrysum , from another Ecklon collection. This taxon, characterised by broad leaves and large capitula in many-headed synflorescences, has been kept separate as Syncarpha chlorochrysum until now.

Selected list of specimens seen (see Supplementary Materials for full list):

South Africa: Western Cape. –3419 (Caledon): ‘ Honingklip Pakskuur, Kleinmond. Natuurbewaring : Veldblomplukbedryf’ , (– AC), 19 Apr 1984, van der Walt 19 ( NBG, PRE) ; Keeromskloof, Salmonsdam Nature Reserve, Stanford , (– BC), 11 Sep 1981, van Wyk 594 ( NBG, PRE) ; Baardscheerdersbosch , (– DA), 28 Dec 1946, Compton 19,023 ( NBG) ; ‘ In collibus prope Elim’ , (– DB), Oct 1894, Bolus 6916 ( NBG, PRE) . – 3420 (Bredasdorp): De Hoop Nature Reserve , 150 m outside reserve entrance, (– AD), 5 Dec 2007, Bennett, Pekeur & Wolfson 3601 ( NBG) ; ‘ aan die suidwestelike kant van die Potberg Opvoedkundige Sentrum’ , (– BC), 24 Sep 1983, 3rd Ekskursie U.S. 3 ( NBG) ; Potberg Estates, near Cape Infanta , (– BD), 16 Jun 1974, Bayliss 6583 ( NBG) ; 1.2 m N.W. of Arniston , (– CA), 14 Dec 1962, Acocks 23,138 ( PRE [2 sheets]) ; mountain above Bredasdorp Village on north slopes, (– CA), 9 Nov 1971, Barker 10,863 ( NBG [two sheets]) ; Struisbaai, ridge above town in undeveloped area between Die Plaat and old abandoned water tower, (– CC), 6 Apr 2004, Bergh 1257 ( NBG) ; ‘ In montiubs pone Koude Rivier prope ElimBredasdorp , (– DA), 3 Dec 1896, Schlechter 9601 ( BOL) . – 3421 (Riversdale): ± 12 km N from Stilbaai on roadside, (– AB), 12 Apr 2011, Haiden 35 ( NBG [two sheets]) ; Riversdale , (– AB), Nov 1932, Fergusen s.n. ( BOL 46756 ) ; 2 m. S of Vermaaklikheid P.O., (– AC), 25 Oct 1968, Acocks 24,126 ( PRE) ; Riethuiskraal road, Still Bay , (– AD), 24 Jan 1980, Bohnen 7301 ( NBG, PRE [2 sheets]) .

Figures

Fig. 4. Achyranthemum mucronatum. A.Habit.B. Synflorescence, form with large capitula. C.Leaf indumentum (Compton 5559, NBG). D. Capitulum.E.Synflorescence, form with small capitula.F. Distribution.All photographs N.G. Bergh.