Exochaenium natalense (Schinz) Kissling & K.W.Grieve

Kissling, Jonathan, Grieve, Kate W., Grieve, Graham & Bytebier, Benny, 2023, Exochaenium natalense (Gentianaceae), a reinstated taxon endemic to KwaZulu-Natal, South Africa, Phytotaxa 619 (1), pp. 117-122 : 120-121

Exochaenium natalense (Schinz) Kissling & K.W.Grieve , combinatio nova.

Basionym:— Belmontia natalensis Schinz (1894: 220) .

Homotypic synonyms:— Exochaenium grande var. homostylum Hill (1908: 338) .

Sebaea natalensis (Schinz) Schinz (1906:782) , nom. illeg. [non Sebaea natalensis Schinz (1896:442) ].

Type:— SOUTHAFRICA. KwaZulu-Natal, Clairmont, 5 Aug. 1893, Schlechter 3060 (Lectotype Z [ Z000070706 ]!, hic designatus; isolectotype Z [ Z000070705 ]!) .

Nomenclatural notes: —There are two sheets of Schlechter 3060 at Herb. Z. One [Z000070706] contains five stems each with a single flower, whereas the other [Z000070705] contains a single stem from which the flower is removed and stored in a pocket. These two specimens should be considered as duplicates and thus a lectotype needed to be chosen, in accordance with the International Code of Nomenclature for algae, fungi and plants Arts 8.2 and 8.3 ( Turland et al. 2018). The first author (JK) has studied the type material in detail and confirmed that both sheets represent the same taxon. The sheet with five stems contains more and better material and is consequently chosen here as lectotype.

When Schinz transferred Belmontia natalensis to the genus Sebaea in 1906, he clearly forgot that he had already described a different and currently still accepted species, as Sebaea natalensis in 1896. Thus, should Exochaenium natalense ever be transferred to the genus Sebaea , it will need a new name.

Diagnosis: —This species is morphologically closely allied to Exochaenium grande (E.Mey.) Griseb. , but is markedly different in terms of its much smaller flower size of c. 0.8–1.5 cm diameter (vs c. 3.0– 4.5 cm for E. grande ) and the arrangement of the reproductive organs, with anthers positioned at the same level as the stigma (vs distyly in E. grande ), possibly indicating differences in pollination strategies. The species can also be differentiated on the basis of their ecological preferences.

Description: —Annual, erect herbs, 15–20 cm tall. Stems simple, rarely branched from base, sometimes branched above, 4-ridged. Leaves sessile, opposite, 7–20 mm long, 3–6 mm broad, lanceolate, acute at apex, base narrowed, margin entire, basal leaves sometimes reduced. Inflorescence corymbose, lax, single to several flowered. Calyx of 4 or 5 free sepals, each 7–16 mm long, 3–5 mm broad, ovate-lanceolate, acuminate, with conspicuous keel-wing, 2–3 mm broad at semi-cordate base, hyaline, presence of colleters on inside base. Corolla pure white; tube 9.0– 14.5 mm long, infundibuliform; corolla lobes suborbicular, 5.0– 8.5 mm long, 4–5 mm broad, margins entire, apex acuminate. Stamens inserted ± half way up tube, at same level as stigma. Filaments 6.0– 9.5 mm long; anthers, c. 1–2 mm long, each with apical and 2 tiny stipitate basal glands. Ovary ovoid, c. 2–6 × 2–4 mm, bilocular, placentation axile, ovules numerous. Style and stigma 4–18 mm long, filiform. Stigma slightly clavate, papillose. Fruit and seed not seen.

Iconography: — Hill (1908: 317, plate G). See also drawing accompanying plate K000195293 (J.M.Wood 541) from Royal Botanic Gardens Kew.

Distribution: —This species occurs along a section of the eastern coastal region of South Africa. It is found mainly in the Port Edward district, on the border between the Eastern Cape and southern KwaZulu-Natal, South Africa. The range extends northwards to Port Shepstone (Oribi Flats) and uMzinto districts in KwaZulu-Natal. There are historical records from the greater eThekwini [Durban] area and Zululand, localities that have been transformed by urban development and agriculture. The species has been observed by the second and third authors along the eastern seaboard of the Eastern Cape, known as the Pondoland coast, between Port St Johns and the Umtamvuna River, although no specimens have been collected from this region as yet.

Ecology and habitat: — The species inhabits the Indian Ocean Coastal Belt biome, in particular Pondoland-Ugu Coastal Sourveld (CB4) and KwaZulu-Natal Coastal Belt Sandstone Sourveld (CB3) ( Mucina & Rutherford 2006). These vegetation types are characterised by undulating coastal plains, species-rich grasslands, rocky outcrops and forested gullies, at elevations up to 600 m. The area receives mostly summer rainfall with some rain in winter .

Exochaenium natalense and E. grande occur sympatrically although the latter has a much wider distribution. The two species also have different ecological preferences—whereas E. grande is usually found in well drained grassland, E. natalense is always found in seasonally wet to moist grassland (sometimes even in water).

Etymology: —This taxon was named by Schinz (1894), after its geographical origin, previously named Natal and now KwaZulu-Natal, in South Africa.

Conservation status: —This species has a restricted distribution and is endemic to the southwestern region of KwaZulu-Natal. A small part of the region is statutorily conserved and the rest is transformed by agriculture and subsistence farming, infrastructure development and urban sprawl and for these reasons, the area is regarded as being of conservation concern ( Mucina & Rutherford 2006). Exochaenium natalense is a habitat specialist and is fairly uncommon within this region of c. 1230 km 2. Because the extent of occurrence of the species is estimated to be less than 5000 km 2, based on historical collections and the authors’ observations, and because populations seem to be fragmented, and population decline is projected due to habitat loss and degradation, it is suggested that this species should be regarded as Endangered: B1ab(i–iv).

Representative specimens examined: — SOUTH AFRICA. KwaZulu-Natal: Eisdumbeni , 1800 ft., J.M.Wood 133 ( K [ K000195293 ], NH [ NH0004093 -0]); [ Durban ] “ Bei Port Natal ”, 28 Mar. 1832, J.F.Drège s.n. ( P [ P00560847 ]); [ Durban ] Fields Hill , 358m,n.d., H.Evans 190 ( NH) ; Inanda,[Durban district],[252m], J.M.Wood 541 ( K [ K000195293 ], NH [ NH0002056-0 ]); Izinqoleni district: Kwazamane , 394 m, 21 Mar. 2019, K.W.Grieve 2841 ( PRE) ; Margate , [114 m], 4 Feb. 1987, H.B.Nicholson 2561 ( PCE [ PCE0005454 ]) ; Mvoti kloof, Canema estate , 7 Oaks , [2930BA], 20 Jan. 1990, A.Abbott 4999 ( PCE [ PCE0005472 ], NH) ; Oribi , [432 m], Apr.1937, A.McClean 442 ( NH) ; Paddock district, Oribi Flats, Whistling Pine Farm , 482 m, 25 Jan. 2017, K.W.Grieve 2295 ( PCE [ PCE0014180 ]) ; Port Edward, Red Desert Nature Reserve coastal section, 10 m, 8 Dec. 2015, K.W.Grieve 1886 ( NU [ NU0088250 ]) ; Port Edward, Red Desert Nature Reserve coastal section, 17 m, 23 Feb. 2017, K.W.Grieve 2322 ( PCE [ PCE0014181 ]) ; Port Edward, Red Desert Nature Reserve coastal section, 24 m, 6 Jan. 2022, K.W.Grieve 3078 ( NH) ; Port Edward, Izingolweni roadside, [3130AA], 2 Jan. 1965, O.M.Hilliard 3038 ( NU [ NU0092021 ]) ; Port Edward, Umtamvuna Nature Reserve , [350 m], 14 Apr. 1982, H.B.Nicholson 2248 ( PCE [ PCE0005455 ]) ; Port Edward, Umtamvuna Nature Reserve , Clearwater , [350 m], 3 Mar. 1983, A.Abbott 880 ( PCE [ PCE0005451 ]) ; Port Edward, Umtamvuna Nature Reserve , [350 m], 13 Mar. 1984, A.Abbott 1827 ( NH, PCE [ PCE0005450 ]) ; Port Edward, Umtamvuna Nature Reserve, Office [Beacon Hill], [350 m], 12 Feb. 1986, A.Abbott 2982a ( NH, PCE [ PCE0005449 ]) ; Port Edward, Umtamvuna Nature Reserve , [350 m], 31 Mar. 1995, A.Abbott 6740 ( NH) ; Port Edward, Umtamvuna Nature Reserve, Beacon Hill , [350 m], 2 Mar. 1997, C.J.Potgieter s.n. ( NU [ NU0092023 ]) ; Port Edward, Umtamvuna Nature Reserve , western heights, 365 m, 9 Feb. 2017, K.W.Grieve 2306 ( PCE [ PCE0014179 ]) ; uMzinto district, Vernon Crookes Nature Reserve , 449 m, 7 Feb. 2019, K.W.Grieve 2801 ( PCE [ PCE0013839 ]) ; Uvongo sandflats, [19 m], 19 Dec. 1965, R.Strey 6181 ( NH) ; Zululand, Hlabisa district, Lake St Lucia , east shore [2832AB], 5–10 m, 30 Apr. 1974, R.H.Taylor 175 ( NU [ NU0092020 ]) ; Zululand, Lake Nhlabane , 5 Jan. 1992, C.J.Ward & A.Rajh 11674 ( UDW [ UDW13406 ]) ; Zululand, “ N’goya ” [oNgoye, 2831DD], 1000–2000 ft., 18 Mar. 1904, J.M.Wood 9322 ( K [ K000195292 ]) .