Erica arida R. D. Hoekstra, 2025

Hoekstra, Rendert D., Musker, Seth D., Pirie, Michael D. & Vlok, Jan H. J., 2025, An integrative approach to alpha taxonomy in Erica L. (Ericaceae) with three new species from the Western Cape, South Africa, PhytoKeys 257, pp. 95-117 : 95-117

Erica arida R. D. Hoekstra sp. nov.

Fig. 4

Link.

WFO: https://list.worldfloraonline.org/wfo-1000079209.

Type.

South Africa • Western Cape, 3320 DD (Warmwaterberg): Langeberg Range, Barrydale outskirts, on steep middle south-facing slopes north of the Doringrivier Catchment Area , 709 m, 33.922°S, 20.779°E, 14 February 2024, R. D. Hoekstra 218 ( NBG, holotype) .

Diagnosis.

Erica arida matches characters exhibited in E. tenuicaulis , from which it differs in leaf shape (saddle-shaped, as opposed to broadly linear in E. tenuicaulis ), its straight style (curved in E. tenuicaulis ) and staminal filaments approximately 3 times as long as the anthers (as long as the anthers in E. tenuicaulis ).

Description.

Rounded to semi-spreading, resprouting shrublet up to 30 cm tall, rootstock thick. Branches twiggy, erect, glabrous; secondary branches erect or ascending, sparsely stipitate-glandular. Leaves 3 - nate, erect to spreading, ovate to subcordate, saddle-shaped, blades 2.5–4.0 × 1.0– 1.5 mm, acute; adaxially convex, glabrous, margins revolute, rarely sparsely ciliolate; abaxially deeply sulcate, densely hispidulous within sulcus with simple, eglandular hairs; petiole ± 1 mm long, occasionally loosely decurrent, margins ciliolate. Inflorescence of 3 - nate flowers at ends of short side branches; pedicel 3.0–4.0 mm long, pale green to pink, viscid, sessile- and stipitate-glandular; bracteoles 2, opposite, median to submedian, oblong to shortly lanceolate, ± 0.75 mm long, subacute, sessile-glandular, glabrous but margins sparsely ciliolate at base, green and slightly sulcate towards abaxial apex; bract partially recaulescent, submedian, lanceolate, acute, sessile-glandular, margin sparsely ciliolate towards base. Calyx 4 - lobed, sepals connate at base, lanceolate, 1.25–1.5 mm long, acute; abaxially glabrous, apex sulcate, the sulcus shortly villous; adaxially glabrous; margins sessile-glandular. Corolla campanulate to shortly urceolate with slightly constricted throat, 3.0–4.0 × 3.0–4.0 mm, white, glabrous, dry; lobes erect to spreading, ± 0.5 mm long, acute, minutely serrated. Stamens 8, free, included, filaments flat, ± 2.5 mm long, glabrous, white turning golden reddish distally; anthers ± 0.8 mm long, obcuneate, dorsifixed at base, bipartite, thecae erect, free, muticous, dark brown; pore ± 0.3 mm long, oval. Ovary 4 - locular, shortly oblong, ± 0.8 mm long, slightly emarginate, red to purplish, hispid with long, simple, eglandular hairs; ovules ± 20 per locule; placenta apical; nectaries basal, green; style ± 3.5 mm long, glabrous, pale pink turning dark red or black towards stigma, exserted; stigma dark red to black, subcapitate. Fruit and seeds not seen. Flowering time: December to February.

Distribution and habitat.

Erica arida is known only from the mountains north of the Doringrivier Catchment Area east of Barrydale in the Western Cape. It has been recorded from a ridgeline at an altitude of 1190 m in Northern Langeberg Sandstone Fynbos ( Mucina and Rutherford 2006), growing in association with Erica barrydalensis , as well as on the middle south-facing slopes as low as 516 m growing in association with Phylica mairei , Erica vestita and Cliffortia pulchella . It has not been recorded from the north-facing slopes.

Threat status.

Erica arida is only known from a few records on iNaturalist and our single collection from the Doringrivier Catchment Area. The three known subpopulations appear to be small and scattered within the catchment area, and our survey at the type locality revealed only 17 plants. Erica arida was found to have an AOO of 12.00 km 2 and an EOO of 12.00 km 2. Additionally, the marshland in the catchment area is heavily infested with invasive Hakea sericea with a significant encroachment up to the middle south-facing slopes where E. arida occurs. This poses a major threat to the two subpopulations on the middle slopes. The habitat of E. arida is remote and difficult to access and only limited botanical surveys have been performed around the catchment area. Therefore, there are not enough data to accurately estimate the population size of this species. However, the wide range in altitude between the known subpopulations and results from our survey suggest that additional small subpopulations may exist within this catchment area. Since all observed subpopulations have consisted of only a few plants we estimate a minimum total population of 100 plants. Based on this estimate, an EOO of 12.00 km 2, ongoing decline in quality of habitat as a result of invasive alien plant species, and its restriction to a single known location, we recommend an IUCN (2012) category of Critically Endangered (CR) under criterion B 1 ab (iii) for E. arida .

Pollination syndrome.

Erica arida has well-developed nectaries and small, open cup-shaped flowers, suggesting entomophily. The lack of a peltate stigma and the fact that pollen is not released in a cloud after in situ manipulation make anemophily highly unlikely, and the size and shape of the corolla make ornithophily unlikely.

Etymology.

Erica arida is named for the seasonal aridity seen during its flowering months in the part of the Klein Karoo where it occurs; from the Latin, arida , for dry or arid.

Subgeneric classification.

The closest relatives of E. arida are classified in at least five different (non-monophyletic) sections, but most are in either Ceramia (glabrous, pitcher-shaped corollas and terminal inflorescences: consistent with E. arida ) or Arsace (large peltate stigmas: inconsistent). Placement of the new species in Ceramia may be a useful provisional classification.

Notes on morphology and phylogeny.

The single strict match for E. arida with the Erica ID aid, E. tenuicaulis , diagnosed above, has yet to be analysed phylogenetically. Phylogenetic data place E. arida in a clade containing E. cordata , E. lowryensis , E. flanaganii (ITS only), E. hispidula , E. turneri , E. leucopelta , E. natalitia , E. copiosa , E. tradouwensis and E. grata , with which it is unlikely to be confused as it differs from all of these by its glabrous (as opposed to hairy) leaves. It further differs from E. cordata , E. lowryensis and E. tenuicaulis in leaf shape (saddle-shaped, as opposed to cordate in E. cordata , and lanceolate in E. lowryensis ); from E. turneri and E. copiosa by its muticous (as opposed to awned) anthers; from E. turneri by its closed-backed (versus distinctly broad, open-backed) leaves, and glabrous (versus hairy) corolla, and from E. copiosa , E. tradouwensis and E. grata by its glabrous (as opposed to hairy) sepals. Erica hispidula , E. leucopelta and E. natalitia are clearly distinct wind-pollinated plants with peltate stigmas and absent nectaries, in contrast to E. arida which has a subcapitate stigma and conspicuous nectaries.

The placement of Erica flanaganii is unexpected: it is geographically distant, from the Drakensberg Mountains more than 500 km from the eastern edge of the CFR, as well as morphologically dissimilar, possessing a hairy corolla, lanceolate imbricate leaves, a fully recaulescent bract and anther appendages. The result (from data presented by Pirie et al. 2011; 2024) is only shown by ITS and contradicted by plastid results. Additional data from different samples are needed.

Figures

Figure 4. Erica arida R. D. Hoekstra A incomplete inflorescences B glandular pedicel, bracteoles and calyx C dissected flower showing parts of the androecium and gynoecium D whole plant in situ. Voucher R. D. Hoekstra 218 (NBG).