Senegalia ajaya Alam & Lokho, 2024

Senegalia ajaya Alam & Lokho , sp. nov. ( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 , 3 View FIGURE 3 , 4 View FIGURE 4 , 5 View FIGURE 5 & Table 1)

Type:— INDIA. West Bengal: Birbhum District, Ajay River , 220 37′ 34″ N, 870 42′ 32.6″ E, 46 m a.s.l. ; 1 st November 2020; S. Alam 1120 (holotype: CAL; isotype: Visva-Bharati Herbarium, Department of Botany, Visva-Bharati University , Santiniketan , West Bengal) .

Diagnosis:— Senegalia ajaya sp. nov. is morphologically similar to S. caesia , in having a centric petiolule, where the mid vein originates near the centre of the leaflet base. However, it can be distinguished from S. caesia by several key morphological features as follows: its climbing shrub habit ( Figs. 1A View FIGURE 1 & 2A View FIGURE 2 ), the occurrence of prickles on the underside of the leaf rachilla ( Figs.1F View FIGURE 1 & 3A View FIGURE 3 ), two types of paraphyllidia at pinnae bases ( Figs. 1G View FIGURE 1 , 3C & 3D View FIGURE 3 ), 4–6 pairs of pinnae with penultimate pair always having the maximum number of leaflets (1–2 pairs more) ( Fig. 4C View FIGURE 4 ), 5–11 pairs of leaflets per pinna with asymmetrically rounded leaflet bases ( Figs. 4D & 4E View FIGURE 4 ); internode with 6-rows of prickles ( Fig. 4A View FIGURE 4 ), the presence of tendrils on branches ( Fig. 4B View FIGURE 4 ), mid vein extended straight to the apiculate apex ( Figs. 4D & 4E View FIGURE 4 ).

Description:—Climbing shrubs; stems angulate, glabrous; some branchlets modified into tendrils. Internodal prickles in six rows, 0.5–1.5 mm long, recurved, gradually flattened to the base; prickles present on the lower side of the petiole, rachis and rachilla. Stipules caducous, triangular, adpressed-hairy, 3–4 × 2–3 mm, yellowish light green. Leaves bipinnate with 4–6 pairs of opposite pinnae, petiole 30–60 mm long, rachis 30–115 mm long, furrow in the middle, adpressed-hairy; the tip of the rachis extended by a soft and pointed spine-like structure (2–7 mm long); penultimate pinnae pair bearing more leaflets (1–2 pairs more) than the other pairs; leaflets 5–11 pairs per pinna, subsessile, linear-oblong, unequal-sided, free from the adjoining leaflets, 1–1.5 × 0.4–0.7 cm, with dark green upper surface, glabrous, and light green lower surface, puberulous; apex mucronate, straight; base asymmetrically rounded; mid vein placed centrally at base and running close to the upper margin, extended straight to the apex; a second prominent vein diverging from the base and extending to 2/3 length of each leaflet. Two types of paraphyllidia (normal and special) at pinnae bases: normal type with two-minute rudimentary appendages (1–2 mm long) subtending from each pinna pulvinus of lowermost 1–3 pairs of pinnae; special type consisting of a small rudimentary appendage and one diminutive leaflet (5–8 × 2–4 mm), subtending from each pinna pulvinus of uppermost 1–3 pairs of pinnae, mid vein central at the base and running close to the lower margin up to the apex. Petiole gland situated near the base, 10–15 mm above the leaf base, 0–1 mm above the pulvinus, oblong, 2–5 × 1.5–3 mm, asymmetric, prominently raised at distal end, smooth when fresh, longitudinally wrinkled when dry; rachis glands situated at or near the bases of the uppermost 1–3 pairs of pinnae, small, circular, 1.5–2 × 1.5–2 mm, sessile; rachilla glands situated near the base of the uppermost 1–2 pairs of leaflets in the uppermost 1–3 pairs of pinnae, minute, 1–1.5 × 1–1.5 mm, sessile. Inflorescences comprising 4–6 pedunculate heads arranged in terminal panicles; peduncles 11–20 mm long, adpressed hairy. Flowers sessile, ebracteate, creamy white, 35–45 flowers per head; calyx 1.5–2 mm long, gamosepalous, lobed, reddish, half of the length of petals; petals 5, gamopetalous, 2–3 mm long, white. Stamens 3–5 mm long, numerous. Ovary stipitate, style 3–6 mm long. Pods linear-oblong, 6.5–9.5 × 1.4–1.7 cm, flat, glabrous, 5–10 seeded, thinly coriaceous, scarcely raised over seeds along midline, deep brown (fresh) to light brown color (dry), dehiscent, splitting into two valves at maturity, apex acute, base narrowed to a short stipe. Seeds spherical, flattened, 5–8 × 4–7 mm, dark brown.

Habitat:—Beside the riverbank of Ajay climbing over the host plant Phoenix sylvestris ( Linnaeus 1753: 1189) Roxburgh (1832: 787) .

Phenology:—Flowering in October to November; fruiting in December to February.

Etymology:—The species epithet ajaya is named after the river Ajay, as the type specimens were collected on its riverbank from Birbhum district, West Bengal, India.

Local name:—Khebla (Bengali).

Distribution:—Ajay Riverbank, Birbhum, West Bengal, India ( Figure 5 View FIGURE 5 ).

Conservation Status:—Data Deficient (DD), according to IUCN (2024). The new species was found in one location and further inventory/exploration is necessary for its actual assessment. In fact, in many cases newly described species are at first known from a single location (the locus classicus), but based on the detected threats and possible population trends, they are attributed to very different threat categories, as Critically Endangered (CR) ( Yan & Hao 2024), Endangered ( Brullo et al. 2015), Vulnerable (VU) ( Swanepoel et al. 2021), Near Threatened (NT) ( Perrino et al. 2018), Data Deficient (DD) ( Chinchilla 2020).

Threats:—A single plant was discovered beside the river bank of Ajay in Birbhum district, West Bengal, India. The area is usually visited by a large herd of cattle to graze around and they are the potential threats to the plant. However, due to the presence of the prickles on the underside and glands on the upper side of the petiole, rachis and rachilla in S. ajaya as high level of defense mechanism, the cattle are not attracted to the plant and stand safe.

Taxonomic notes:—In genus Senegalia , the internodal prickles are typically found on the stems and branches besides on the lower side of the petiole and rachis, however, these prickles never extend to the pinna rachilla in any recorded Senegalia species. The presence of prickles on the lower-side of the rachilla of S. ajaya is a distinctive feature, unique among Senegalia species both in India and in the world. The presence of paraphyllidia at the base of pinna is the characteristic feature of the neotropical genus Acaciella Britton & Rose (1928: 96) . Similar structure is found in South American species Senegalia olivensana (G.P. Lewis 1996: 372) Seigler & Ebinger (2006: 61) . On the other hand, the presence of paraphyllidia in Indian Senegalia species was not recorded earlier. There are two types of paraphyllidia found in S. ajaya , the normal type with two-minute rudimentary appendages (1–2 mm long) subtending from each pinna pulvinus of lowermost 1–3 pairs of pinnae; the special type consisting of a small rudimentary appendage and one diminutive leaflet (5–8 × 2–4 mm), subtending from each pinna pulvinus of uppermost 1–3 pairs of pinnae, mid vein central at the base and running close to the lower margin up to the apex.