Astragalus pseudoanisacanthus A.Khan, A.Sultan & Zarre, 2023

Khan, Amjad, Sultan, Amir, Zarre, Shahin & Ishaq, Kamran, 2023, Astragalus pseudoanisacanthus, a new species of section Poterion from northern Balochistan (Pakistan), Phytotaxa 622 (4), pp. 236-251 : 237-243

Astragalus pseudoanisacanthus A.Khan, A.Sultan & Zarre , sp. nov. ( Figs. 1‒4 )

Holotype: Pakistan, D6, Balochistan, Zhob district, Ahmadzai Mountain, Babarh Kalay , 31.33833312 N, 69.4875785 E, 2000‒2300 m a.s.l., 26 March 2022, Amjad Khan & Kamran Ishaq 102516 ( RAW!).

Diagnosis

Astragalus pseudoanisacanthus is closely related to A. anisacanthus , but differs in having relatively shorter corolla (standard up to 12.5 mm versus 12‒18 mm), white corolla (versus corolla pinkish to purplish), legume semi-bilocular, 2‒4-seeded (versus legume unilocular, 1‒2-seeded) ( Tab. 1 ).

Description

Plant spiny shrub 25‒35 cm tall, mostly loosely branched at the base. Hairs white 0.2‒0.5 mm. Stem of the current year 8‒13 cm, 3‒6 mm thick; bark brownish, internode 4‒8 mm, tomentose, many branches arise from the base. Brachyblasts at the main stem densely tomentose and sometimes glabrescent with age. Stipule of the main stems white membranous, 1‒2-nerved, 4‒6 mm, basal 2.5‒4 mm adnate to petiole, free part 1.5‒2 mm, half embracing the stem, triangular, densely tomentose. Leaves of the main stems, 1.5–3 cm, obliquely to horizontally spreading; petiole 0.4–1.3 cm, in the young leaf sparsely subappressed hairy, rachis 0.8–1.7 cm, thin or rigid, terminal spine 1.5–5.5 mm. Leaflets in 3–4 (–5) pairs, basal leaflets longer, oblanceolate, 2.5–9.0 × 1.5–3.0 mm, the upper ones smaller and obovate, all shortly mucronulate to mucronate, with a cusp 0.2–0.5 mm, densely to sparsely pilose on both sides. Leaves of the brachyblasts 2‒5.5 cm, with a petiole 0.5–2.5 cm; leaflets in 3–5(–6) pairs, 1.5–7.5 × 1–3.5 mm, round to obovate, flat or sometimes oblanceolate, short mucronulate with a cusp 0.1–0.3 mm, densely covered on both sides with appressed or subappressed hairs upto 0.5–0.7 mm. Peduncle 1–3.0 cm sparsely covered with spreading hairs or sometimes subappressed hairs. Racemes 3–5 flowered, axis 12–33 mm. Bracts 1.5–3.0 × 0.5–2.0 mm, whitish membranous, ovate to lanceolate, acute, faintly 3-nerved, sparsely subappressed hairy. Pedicels 1.5–3.0 mm, pilose with spreading white hairs. Bracteoles 1–1.5 mm, white membranous, linear, densely pilose. Calyx at beginning of anthesis tubular, 5.5–9.5 mm long, 2.5–4.5 mm wide, yellowish green or cream coloured, at fruiting time becoming inflated or bladderyenlarged, more or less ellipsoid, 8.5–12 mm long, 6.5–9 mm wide, with 8–12 reticulately connected parallel nerves, densely subappressed pilose at anthesis later on loosely covered with subappressed to spreading hairs, calyx teeth subulate basally somewhat triangular, 2.0–3.0 mm, subequal, pilose with spreading hairs. Petals white, claws connate at the base with stamen tube. Vexillum 9–12.5 mm, blade obliquely recurved, 5–6.5 × 4.0– 4.5 mm, obovate, retuse or emarginate at the apex, cuneate, claw 6–7 mm. Wings 9–12 mm; blade narrowly oblong to elliptic or obtuse, often slightly emarginate, 4.5 × 1.5 mm, auricle 0.4–0.5 mm, claw 7.5–8.5 mm. Keel 9–10.5 mm; blade obliquely obovate-triangular, with widely to subrectangularly curved lower edge and slightly concave upper edge, subacute, 3.5–4.5 × 1.5–2 mm, auricle short upto 0.2× 0.3 mm, claw 6–7.5 mm. Stamen tube 10–12 mm, truncate at the mouth, apically curved, free part of filaments alternate short (ca. 3 mm) and long (3.5 mm). Ovary with a 0.9–1.2 mm stipe, narrowly ellipsoid, densely subappressed hairy with short white hair, style glabrous, often sparsely pilose at the base. Legume with a 1–1.5 mm stipe, 6–8 mm long, 2–3 mm high and 3–4.5 wide, coriaceous-papery, ellipsoid, with a beak 1–1.5 mm; partially bilocular; valves cream-coloured, covered with subappressed white hair upto 0.5 mm. Seeds 2–4, 1.5– 2.5 × 1.0– 1.5 mm, triangular reniform, light brown, granulate.

Etymology: The species epithet refers to its similarity in general appearance to its closely allied species, i.e. A. anisacanthus .

Phenology: Flowering from March to April and fruiting from April to May.

Geographical distribution

Based on current known distribution A. pseudoanisacanthus is endemic to Balochistan. It is only known from one population in the type locality, growing along dry slopes of Ahmadzai Mountain near Babarh village in Zhob district ( Fig. 5 ). Phytogeographically most species of Astragalus sect. Poterion are confined to the Irano-Turanian region. Iran is regarded as center of diversity for this section with 9 out of 12 species (75 %), of which four species are exclusively endemic to the country.

Ecology

Astragalus pseudoanisacanthus inhabits mixed community comprising Olea europaea subsp. cuspidata (Wall. & G.Don) Ciferri (1942: 96) and Pistacia atlantica Desfontaines (1799: 364) , along mountain slopes and tracks, at an elevation of 2000‒2300 m a.s.l. The other associated taxa include Nepeta praetervisa Rechinger (1979: 8) , Salvia santolinifolia Boissier (1844: 13) , Cousinia haeckeliae Bornm ̧ller in Friedrich (1938: 40), Astragalus stocksii Bentham ex Bunge (1868: 6) , Astragalus hostilis Boissier (1872: 306) , Ebenus stellata Boissier (1843: 100) , Withania coagulans (Stocks) Dunal (1852: 685) , Sophora mollis (Royle) Graham ex Baker (1878: 251) , Jurinea berardioides (Boiss.) Hoffmann in Engler & Prantl (1893: 321), Pteropyrum aucheri Jaubert & Spach (1844: 8) , Cistanche tubulosa (Schenk) Wight ex Hooker (1884: 324) , Acantholimon lycopodioides (Girard) Boissier (1848: 632) , and Aristida cyanantha Steudel (1854: 141) .

Conservation status

Astragalus pseudoanisacanthus is endemic to Balochistan and is currently known only from a single collection from the type locality. Its habitat is affected by intense anthropogenic activities like heavy grazing by livestock especially, sheep and goats. Local inhabitants uprooted the plants for consumption as firewood. Other threats include road constructions, land sliding and soil erosion due to intense floods. Given the small population size A. pseudoanisacanthus is considered to be facing an extremely high risk of extinction in the wild and is provisionally assessed as critically endangered, CR B1ab (i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v), according to the IUCN (2022) red listing system, as similar cases in different genera and families on various continents have often been attributed to the same threat category (e.g. Perrino & Calabrese 2018; Wagensommer & Venanzoni 2021; Ngoc et al. 2022; Zhigila & Muasya 2022), further explorations in the area are recommended, to determine its population size and to better evaluate the conservation status, as already suggested in research works with a scientific approach on plant species at risk of extinction (e.g. Perrino 2011; Ren et al. 2012; Perrino et al. 2013; Walsh et al. 2019).

Figures

FIGURE 1. Astragalus pseudoanisacanthus A. Khan, A. Sultan & Zarre (A) Habitat, (B–C) Habit. (D–F) Flower and fruit close up.

FIGURE 2. Astragalus pseudoanisacanthus (A) Habit from the holotype, (B) Stipule. (C) Inflorescence, (D) Bract, (E) Calyx, (F) Vexillum, (G) Wings, (H) Keel.

FIGURE 3. Astragalus pseudoanisacanthus (I) Keel, (J) Stamina, (K) Pistil, (L) Fruit in inflated calyx, (M–N) Pod indumentum, (O–P) Dehisced pod, (Q) Pod opened to show partial septum, (R) Seeds.

FIGURE 4. Astragalus pseudoanisacanthus (A) Flowering branch, (B) Stipules, (C) Leaf, (D) Bract, (E) Calyx, (F) Vexillum, (G) Wings, (H) Keel, (I) Stamina, (J) Pistil, (K) Pod.

FIGURE 5. Distribution map of Astragalus pseudoanisacanthus in Zhob district, Balochistan.

Tables

TABLE 1. Diagnostic characters of Astragalus pseudoanisacanthus and A. anisacanthus.

Taxon characters	A. pseudoanisacanthus	A. anisacanthus
Stipule	2.5‒4 mm adnate to petiole, 1.5–2 free, tomentose, triangular	2–2.5 mm adnate to petiole, c. 2.5 mm free, densely pilose, broadly triangular
Leaves	c. 2–5.5 cm long	5–8 cm long
Leaflets	2.5–9 × 1.5–3 mm, obovate to oblanceolate, apex mucronulate to mucronate, densely to sparsely pilose on both sides	4–8 × 1.5–3 mm, narrowly ovate to orbicular, apex acute to retuse, mucronulate, densely hairy on both sides or pilose along margin only on the upper surface
Inflorescence	Loose raceme, 3–5-flowered, peduncle 1–3 cm long, loosely hairy; bract ovate-lanceolate, acute, faintly 3- nerved, sparsely sub-appressed hairy; bracteoles linear, c. 1–1.5 mm long, white membranous, pilose	Densely to loosely 2‒5-flowered, peduncle c. 6 mm long, pilose; bract ovate, densely pilose; bracteoles 1.5–2 mm long, densely pilose
Corolla colour	White	Pinkish to purplish
Vexillum	obovate, 12–12.5 × 4–4.5 mm	broadly ovate to obovate, 12–18 × 5.5–9 mm
Legume	6–8 × 3–4.5 mm, broadly ellipsoid, partially bilocular, 2‒4-seeded	4–7 × (2.5‒) 3‒5 mm, ovate, unilocular, 1‒2-seeded
Seeds	2–4, 1.5–2.5 × 1–1.5 mm, light brown	1–2, 3.5–4 × 2.5–3 mm, reddish-brown