MCKAYI N.R.Crouch & Gideon F.Sm., 2023

Abstract

A new Cotyledon species, C. mckayi is described from cliffs of the central Tugela River basin in KwaZulu-Natal province, South Africa. Although the flowers of this new species are superficially similar in terms of shape and size to those of C. nielsii, also from KwaZulu-Natal, C. mckayi is readily separable on both vegetative and reproductive characters, from this and all other taxa of Cotyledon that occur naturally in the province. A key to allow identification of fertile material of the Cotyledon species of KwaZulu-Natal is provided.

Type:— SOUTH AFRICA. KwaZulu-Natal province —2830 (Dundee): UMzinyati River, tributary of the Tugela River (–DA), on cliff ledges adjacent to river, 16 July 2023, N. Crouch & A. McKay 1300 (holotype, mounted as two sheets, Herb. NU barcodes NU 0094575! and NU 0094576!).

Distribution and habitat:— Cotyledon mckayi is so far only known from the valley of the UMzinyati River, and along a short section of the Tugela River downstream of its confluence with the UMzinyati, some 20 km east of Tugela Ferry, in central KwaZulu-Natal. This new species has been observed at five separate localities, with a known range of 18 km from north to south along the UMzinyati River valley. Plants occur singly along cliffside rock ledges of these two rivers, on mainly western aspects although plants are always found in the shade of surrounding vegetation.

The entire known natural geographical distribution range (Fig. 3) of the species falls within the MaputalandPondoland Region of Endemism (Van Wyk & Smith 2001: 82–85), and further within the Greater Midlands Centre of Endemism recently recognised by Carbutt (2023). Cotyledon mckayi occurs in soils overlying dolomitic bedrock, at elevations of ca. 450–660 m, within savannah vegetation of Thukela Valley Bushveld (SVs 1) (Rutherford et al. 2006) (Fig. 1F). No localities within the known range are formally protected.

Diagnosis:—Plants of C. mckayi (Fig. 1B) are medium-sized to large, glabrous, perennial succulents with grey-green leaves having a characteristic purple-infusion, that can be separated from C. orbiculata var. oblonga (Fig. 2A) in presenting flowers with tubes that are not swollen about their middle but are rather subcylindrical and shorter (10–14 mm in length rather than 18–25 mm) and in having prominently channelled and keeled linear leaves (to 200 mm long) at maturity, rather than obovate to oblanceolate leaves to a maximum of 140 mm in length. Cotyledon mckayi differs from C. barbeyi (Fig. 2B) in its corolla tubes only very slightly bulging through the calyx lobes rather than prominently so, in tubes being subcylindrical rather than ampullaceous, in its shorter (to 3–4 mm) calyx lobes relative to those found in C. barbeyi (8–10 mm), in having corolla lobes that usually recurve rather than reflex, and in its squarish rather than oblong nectar scales bearing minutely repand and rounded rather than smooth cup-shaped apices.

Description :

Perennial, erect to spreading to leaning, few-branched, succulent shrub to 450–750(–1600) mm tall. 

Roots fibrous. 

Branches 18–25 mm in diam., green at first, becoming greyish brown to grey with age, ascending to horizontally spreading, then gracefully curved upwards, later decumbent under weight of leafy portions, leaf scars obvious. 

Leaves sessile, grey-green, firm, somewhat leathery, succulent, glabrous, with waxy bloom; blade (120–)130–200 × 17–30 mm, purplish-infused, often more so towards the margin, linear-lanceolate when young, elongate-obovate to narrowly cymbiform at maturity; adaxial surface distinctly concave to more rarely planar, sometimes slightly recurved in terminal ⅕; abaxial surface distinctly convex, smooth; margin concolorous to often purple especially in upper ⅔, appearing cartilaginous, straight, continuous; apex acute, very shortly mucronate. 

Inflorescence an erect thyrse, 300–350 mm long, comprising 3–5 dichasia, each with few (5–7) pendulous flowers; peduncle (250–)270– 300(–320) mm long, glabrous, with waxy bloom, with 1 pair of bracts that is soon shed. Pedicels 16–25 mm long. 

Flowers pendulous; buds light green. Calyx green to strongly purple-infused, with slight white-waxy bloom, bloom easily rubbed off, cat claw-like clasping base of corolla tube. Sepals 5, 3–4 × 3–4 mm, basally fused for 1.0– 1.5 mm, deltoid-triangular. Corolla 20–24 mm long, cylindrical to slightly urceolate, marginally widest at base, very slightly bulging between calyx lobes, with waxy bloom externally, glabrous throughout except for small tufts of white hairs where filaments fused to tube; corolla tube (10–) 13–14 mm long, 7–8(–9) mm in diam., uniformly reddish orange or with alternating, longitudinal light green sections under low light conditions; corolla lobes 10–12 mm long, 4–5(–6) mm in diam., reddish orange, linear-lanceolate, recurved, sometimes fully rolled under, apically rounded-acute to acute, minutely mucronate. Stamens 10, in 2 obscure whorls, fused to corolla tube just below middle of tube; filaments free for 12 mm, light whitish green; anthers 3.6 × 1.2 mm, yellow pre- and post-anthesis, elliptic. Pistil consisting of 5 carpels, elliptic, bulged in centre; carpels 15.5 mm long, shiny mid-green, tapering upwards; styles 7–8 mm long, ± connivent to slightly spreading above; nectar scales 1.5 × 1.5 mm, uniformly light greenish yellow, squarish, vessellike turned upwards, minutely repand above, separate, arranged in broken ring. Follicles 15–16 mm long, shiny light green, enveloped in dry, white, purple-infused remains of corolla. Seeds not seen. 

Chromosome number: unknown.

Flowering time:— Cotyledon mckayi flowers mainly in the winter months, June to August in the southern hemisphere.

Eponymy:— Cotyledon mckayi is named for Mr Andrew McKay (born 19 June 1968, Liverpool, England –) (Fig. 1G), a civil engineer, keen amateur field botanist, and succulent plant enthusiast. Aside from discovering this new Cotyledon species, he has additionally greatly increased our understanding of the distribution of the recently described C. nielsii within the province, which he has shown to extend in range from the Umkomaas River in the south through to the Sikoto River in the north, rather than being restricted to the eThekwini metropolitan region as earlier thought.

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 First published in Phytotaxa 632,Dec 2023