Launaea calmadowensis Baldesi & N. Kilian, 2021

Baldesi, Giacomo & Kilian, Norbert, 2021, A new gypsicolous species of Launaea (Asteraceae, Cichorieae) from north Somalia, Phytotaxa 501 (1), pp. 195-200 : 196-199

Launaea calmadowensis Baldesi & N. Kilian , sp. nov. ( Figs. 1 , 2 )

Type:— SOMALIA. Sanaag Region: “Somalia settentrionale, località 38, colline gessose tra Baran [Badhan] ed Erigavo [Ceerigaabo]”, 11 Dec 1970, R . Bavazzano & J . Lavranos (holotype FT [ FT0005965 ]!; isotype B [ B101149126 ]!) .

Species nova Launaeae quercifoliae (Desf.) Pamp. affinis, a qua capitulis ad apicem caudices ramorum solitariis sessilibusque ex foliis vix emergentibus (versus caulibus floriferis pluri-vel multicapitulatis folia caudicis multo excedentibus), involucro minore (10–14 versus 12–16(–19) mm per anthesin et 12–16 versus 14–21 mm in statu fructifero longo), involucri phyllis apice raro albis (versus apice semper albis), receptaculo in statu fructifero minore (4–6 versus (5–) 7–10 mm lato), ligulis florum minoribus (7–10 versus 11–16 mm longis) differt.

Launaea calmadowensis is most similar to L. quercifolia from Northern Africa (north-east Algeria to north-west Libya) but clearly distinguished from the latter species by the solitary capitula sessile at the end of caudex branches and not or barely emerging from the leaves (versus caudex branches shooting forth a few to many-capitulate synflorescence much exceeding the caudical leaves), the involucre of 10 – 14 mm at anthesis and 12 – 16 mm at fruiting (versus 12 – 16(– 19) at anthesis and 14 – 21 mm at fruiting) and the involucral bracts only exceptionally (versus regularly) with white-brickled tip, the fruiting receptacle of 4 – 6 mm (versus (5 –) 7 – 10 mm) in diameter, and the flowers with a ligule of 7 – 10 mm (versus 11 – 16 mm).

Description:—Pauciennial or perennial herb, 10 – 20 cm high, with a branched woody erect caudex covered with bases of withered leaves and branches crowned by rosulate leaves. Latex turning reddish-orange on exposure. Leaves 3–7 × 0.5 – 3 cm, spathulate in outline, shallowly sinuate-dentate with 3 – 4 broad, conspicuously white-cartilagineously dentate segments; lamina leathery (± succulent), with an acute to obtuse apex and attenuated into a semiamplexicaule base; leaf axils with a dense whitish woolly tuft of hairs ( Fig. 2C ), persisting along the caudex. Capitula mostly solitary, sessile, terminating the caudex axes, not or barely emerging from the leaves ( Fig. 2A ). Capitula with c. 30 – 50 flowers. Receptacle at fruiting 4 – 6 mm in diameter. Involucre at anthesis 10 – 14 mm long, slightly elongated after anthesis, oblong at first, finally 12 – 16 mm long and ± globose. Involucre of 15 – 20(– 25) phyllaries ( Fig. 2B ), imbricate, sparsely hairy abaxially, ciliolate along margins especially toward the apex, adaxially shiny, glabrous; apex sometimes with a white prickle and occasionally revolute; outermost phyllaries broadly ovate-acute, 4 – 6 × 2 – 3 mm, the following ovately to broadly lanceolate, the innermost 10 – 12, linear-lanceolate with a thin ± distinctly scarious margin (visible at least in the basal half), subequal at anthesis and fruiting, 10 – 16 × 2 – 3 mm. Flowers with a yellow ligule (dorsally greyish in marginal flowers) of 7 – 10 mm including teeth of c. 0.5 mm, and a tube 5 – 8 mm long; anther tube with the fertile portion 3.7 – 3.8 mm long and apical appendages of 0.2 – 0.3 mm; style branches c. 2 mm long, sweeping hairs yellow. Achenes 2.5 – 3 × 0.3 – 0.5 mm, only the outermost with 5 main ribs, otherwise with 4 main ribs and each accompanied by 2 secondary ribs, cylindrical but ± 4(– 5)-angular and 4(– 5)-horned at the base (main ribs basally exceeding the corpus), greyish brown and ± densely covered with hyaline papillae ( Fig. 2D ). Pappus 9–10 mm long, persistent, dimorphic, of outer downy (curly, of 1 – 2 rows of cells) and setaceous inner rays ( Fig. 2E ).

Distribution and habitat:—The only gathering known to us comes from gypsaceous hills between Baran town (= Badhan, 10°42’50”N, 48°20’5”E) and Erigavo town (= Ceerigaabo, 10°37’N, 47°22’E) in Sanaag Region of Somaliland, a currently de facto independent state in Somalia. Both towns are situated at a distance of c. 100 km on the south side of the Cal Mado (or Calmadow) mountain range and are connected by a road. No further data were reported for “locality no 38”; likely, the collecting locality is somewhere nearby that road and thus at an elevation between 1100 and 1700 m. The geologic substrate in that area is tertiary sedimentary, constituted mainly of Middle–Late Eocene limestones and Early–Middle Eocene evaporites, the latter including extended gypsum deposits ( Hemmings 1966; Abbate et al. 1994). Floristically the Horn of Africa belongs to the Somali-Masai regional centre of endemism, zonally dominated by deciduous Acacia-Commiphora bushland ( White 1983), which is, however, locally replaced by edaphic vegetation types on the gypsum deposits ( Hemmings 1966). Other species collected from the same locality and on the same day are Plectranthus igniarioides Ryding , Reseda amblycarpa Fresen. , Xylocalyx hispidus S.Carter , Kelleronia splendens Schinz and Zygophyllum decumbens Delile.

Etymology:—The specific epithet calmadowensis refers to the Calmadow mountain range in north Somalia where this new Launaea species was collected.

Threat status:—Data are lacking. According to Ullah & Gadain (2016), no up-to-date information is available on the status (habitat integrity vs. fragmentation) of the vegetation. However, the vegetation of north Somalia has suffered since many decades from overgrazing and general overexploitation ( Hemmings 1966; Hullah & Gadain 2016), and climate change most likely worsened the situation possibly increasing frequencies of severe droughts. Launaea calmadowensis was collected to our knowledge only once; although north Somalia is certainly undercollected, this may indicate that the species is only locally distributed or, if more widespread in the region, that its occurrence is only scattered and rather rare. The threat status of this species should therefore be assessed in the future; currently it must be classified as data deficient (DD) ( IUCN 2019).

Significance and relationship:—The Asteraceae are a family particularly rich in endemics in Somalia. Based on Thulin (2006), 56 or c. 35 % of the c. 160 indigenous species of Asteraceae are endemic to Somalia; considering only north Somalia, 45 of 120 species or 37.5 % are endemic. The recent addition of a new species for a genus of Asteraceae endemic to the Flora of Somalia confirms this richness ( Baldesi et al. 2020). An important reason for this high endemism certainly is the wealth of suitable habitats for a family, the members of which are predominantly present in open types of vegetation.

The diversity of open habitats also includes extensive areas (c. 36 000 km 2) of anhydrite deposits (gypsum) in the eastern and southern parts with a specialised vegetation of gypsum-tolerant associations ( Hemmings 1966). Three Launaea species ( L. hafunensis , L. crassifolia , L. lackii ; Kilian 1997) were so far known to occur there on gypsum hills. Launaea calmadowensis now provides a further example. In conformity with a general trend to succulence in gypsicolous plants ( Escudero et al. 2015), Launaea species on gypsum are usually characterised by leathery succulent and often glaucous leaves with weakly dentate margins. This is most apparent in species with a wider distribution and lower substrate specificity such as L. crassifolia ; on substrates other than gypsum, its leaves are thin and soft and their margins are strongly dentate or denticulate ( Kilian 1997). Most species of Launaea found on gypsum are to be classified with the terminology of Escudero et al. (2015) as gypsovags, thus plants that can grow both in gypsum and non-gypsum substrates. Our knowledge of the habitat preferences of L. calmadowensis is too limited for a conclusion, therefore the only species in the genus that is with some certainty actually confined to gypsum and thus a true gypsophile is L. quercifolia , the species morphologically nearest to L. calmadowensis . Its distribution spans the eastern part of another large gypsum habitat area situated in North-Western Africa ( Escudero et al. 2015: fig. 2A) between Biskra in Algeria and Mizda in Libya.

The morphological similarity between both species is clearly not superficial, although leaf features and possibly also the small somehow arbuscular caudex should be considered as adaptations to the gypsum substrate, which thus may perhaps have evolved in parallel. Besides that, the two species share the achene and involucre features highly diagnostic for Launaea sect. Zollikoferia and, in addition, the (sub)globose capitula and predominantly angular achenes of the L. angustifolia group ( Kilian 1997), which was corroborated in an initial ITS phylogeny as monophyletic (Kilian unpubl. data). The hypothesis of a close relationship between L. calmadowensis and L. quercifolia therefore seems justified. North-Western Africa and the Horn of Africa / South Arabian Region are parts of the two-pronged diversity centre of the genus ( Kilian 1997) but, remarkably, both do not share a single species.

The habitual difference between the two species is a result of the acaulescence of the caudex axis in Launaea calmadowensis : the flowering shoot that terminates the caudex axis is reduced to a single sessile capitulum; its growth is continued by persisting, crowded or rosetted leafy, lignescent branches from axiles of caudical leaves, which overtop its axis of origin, are themselves terminated by a single capitulum and subsequently overtopped by lateral caudical branches ( Fig. 2A ), etc. Such acaulescence can usually be interpreted as an adaptation to harsh environments, which may be true also in this case. In L. quercifolia , in contrast, the caudex axis is terminated in a well-developed, herbaceous short-lived flowering stem. With respect to the number and size of its leaves, its branching and capitulum number, the flowering stem shows, however, much variation; the delimitation between persisting caudical and short-lived flowering shoot axis is, moreover, often gradual, showing a transitional frequently perennating portion with still rather closely situated leaves.

Figures

FIGURE 1. Launaea calmadowensis, holotype at FT.

FIGURE 2. Launaea calmadowensis. A. Branched caudex axes each with a terminal solitary sessile capitulum, scale bar = 5 cm; B. Involucre; C. Caudical leaf axils with whitish woolly tuft of hairs; D. Achenes densely covered with hyaline papillae; E. Dimorphic pappus of outer downy and setaceous inner rays.