Cyperus kilelai Mesterházy & Reynders, 2024

Mesterházy, Attila, Reynders, Marc & Ngoy Shutcha, Mylor, 2024, Cyperus kilelai (Cyperaceae), a new species from a thermal spring in Katanga (Democratic Republic of the Congo), Plant Ecology and Evolution 157 (3), pp. 336-342 : 336-342

Cyperus kilelai Mesterházy & Reynders sp. nov.

Figs 1 , 2 , 3

Type.

DEMOCRATIC REPUBLIC OF THE CONGO • Haut-Lomami , Upemba region, 22 km SW of Kanonga village, edges of a thermal spring called “ Mayi ya moto ” (which means warm water in Swahili); 09 ° 22 ’ 44 ” S, 25 ° 59 ’ 08 ” E; 665 m; 26 Jun. 2018; J. Kilela 25; holotype: LSHI; isotypes: BR [ BR 0000026212845 V]; BP .

Diagnosis.

This small tussocky species differs from all other Cyperus species by the combination of (weakly) 3–4 angled nutlets of the laterally compressed dimerous type, pale glumes 2.5–3.2 mm long, and an ecological restriction to mineral-rich thermal springs.

Description.

Small annual or tussocky perennial. Culms many per tussock, erect, 20–37 cm long, new ones originating from higher nodes of older culms. Leaf blade filiform, 2–23 cm long × 0.3–1 mm wide, the lower ones often reduced to their sheaths. Inflorescence a single (or two) sessile clusters of 3–6 spikelets (rarely a single spikelet). Involucral bracts usually two, spreading to erect, 0.5–7 cm long. Spikelets 6–24 × 1.8–2.5 mm, lanceolate, rachilla 0.4–0.5 mm wide, slightly zigzag, persistent. Glumes not closely imbricate, 2.5–3.2 × 0.8–1.2 mm, deciduous, strongly concave, yellow to light brown, elliptic, flanks veinless, without hyaline margin, obtuse with pale, 3 - veined midrib reaching the tip. Stamens 2, anthers yellow, 1–1.4 mm long. Stigma branches 2, in ad- and abaxial positions. Nutlet dark-brown, obovate, variable with 3–4 angles (often 1 strong and 3 weaker), apiculate, 1.2–1.5 × 0.5–0.7 mm, smooth, epidermal cells slightly elongated, without silica bodies.

Distribution.

Endemic to the south-east of the Democratic Republic of the Congo. Currently, this species is only known from its type location. As botanical studies have not yet been performed in many of the hot springs in the Upemba graben and new springs are still being discovered ( Odhipio et al. 2020), this species may have a much larger range. The case of C. fontinalis , which has been collected from southern D. R. Congo, Zambia, and Central Madagascar shows that strongly disjunct hot spring habitats are possible for similar species ( Reynders 2013). Within the Zambesian phytochorion, several other rift related regions possess many hot springs that could be suitable habitats for C. kilelai : the Zambezi rift on the border of Zambia and Zimbabwe and the graben of the Sabe river in eastern Zimbabwe ( Gerald et al. 1965).

Habitat and ecology.

The species is locally abundant and monodominant, growing in patches of 1 to 3 metres on wet mud along the edge of the thermal spring (“ Mayi ya moto ”). Its regrowth from higher nodes of older culms allows it to overcome addition of sediments by water or wind. The thermal spring where C. kilelai grows is very hot, with a temperature about 70–80 ° C at the source. Cyperus kilelai occurs at the sites where the water is cooler, at about 30–40 ° C. The soil is white due to the deposition of carbonate minerals and the soil layer on the bedrock is shallow. The species becomes less abundant when the mineral concentration and temperatures are decreasing, approx. 25–30 m from the spring. These springs are further relatively species poor, dominated by grass-like plants, except some palms and small trees. In higher areas, C. kilelai is replaced by Imperata cylindrica (L.) P. Beauv. ( Poaceae ) and Cyperus laevigatus L.

Phenology.

The type collection was made in June during which both flowering and fruiting culms were observed. Most likely the phenology of this species is similar to other Cyperaceae species in this region: it starts flowering shortly after the rainy season periods. Presumably, the flowering period lasts from May to July. Although C. kilelai primarily seems to be a perennial species inhabiting permanently wet soils, it is very likely to have a short generation cycle which allows it to survive drier periods as an annual.

Etymology.

The species name commemorates Jacques Kilela Mwanasomwe, a plant ecologist of the University of Lubumbashi, who collected the type material of the species.

Preliminary IUCN conservation assessment.

Vulnerable: VU (D 2). Cyperus kilelai seems to be a restricted species, which is only known from the type locality in the southwest corner of the Upemba graben, about 17.5 km south of lake Kabwe. The Upemba graben is very rich in thermal springs and these Rift-related springs are in general characterized by their high temperature and sulphurous-carbonated chemical composition ( Mathieu 1912; Odhipio et al. 2020). Brine springs containing chloride are also present but very scarce in the Upemba region (Salines de Ganza near the Kanandula river, see Van Meel 1966). These are more common in the south of Katanga due to the likable presence of a precambrian halite evaporative deposit, but the latter springs are generally much colder ( Buffard and Grujenschi 1979). Although many thermal springs in the Katanga region were visited by botanists (Jean Jacques Symoens, Gaston François de Witte, Stanisław Lisowski) during the 20 th century, our new taxon did not appear in their collections. Deep botanical and vegetation researches were done only in the south of Katanga, in the salt springs of Mwashya ( Symoens 1953; Malaisse 1988), where C. kilelai does not seem to be present. Therefore, we think that even if it would occur in other thermal springs, this must be a rare species, and the local area of occupancy would always be very limited. The single known population is estimated to grow over an area of approx. 1600 m 2, with a population size between 250 and 1000 mature individuals. The type locality of C. kilelai is located outside of the Upemba National Park near several small villages (Saka, Kakesa), where farming families live. The local people consider the thermal spring as a holy place, where ancestors and extra-human powers are present and they therefore do not disturb it. In addition, this spring can be found on a hard bedrock where the salt cover is thin and probably poor in chloride. Therefore, it is unsuitable for salt exploitation. However, the locality is situated in a study area for the installation of large geothermal power plants, especially the very hot springs of the Upemba graben are of high interest ( Makuku 2019; Odhipio et al. 2020). Based on this, the only known location for C. kilelai , and other locations in the region where the species may occur are potentially highly threatened by human activities in the near future. Another potential threat are the use and alteration of these thermal spring for bathing. For example, in Antsirabe (Central Madagascar), at the type locality of Cyperus fontinalis , a spa hotel was built shortly after the collection of this species, as was annotated on the type specimen. Also, the other thermal springs around the town are adjusted and exploited for bathing and in none of these locations, C. fontinalis was found during the expedition of Larridon et al. in 2010 ( Reynders 2013). However, exploitation for bathing does not seem to be a common or traditional practice in the Katanga region but might gain interest in the future, especially in touristic locations. Due to the small population size, the small AOO and EOO, and the presence of a future threat, we assess C. kilelai as Vulnerable (VU), following criterion D 2 ( IUCN Standards and Petitions Committee 2024).

Figures

Figure 1. Morphological characteristics of Cyperus kilelai. A. Plant habit. B. Plant base. C, D. Inflorescence. E. Spikelet. F, G. Details of the rachilla. H. Glume. I, J. Nutlets. Drawn from J. Kilela 25 (BR) by Marc Reynders.

Figure 2. SEM photographs of Cyperus kilelai. A, B. Nutlet. C. Detail of the nutlet epidermal cells. Taken from J. Kilela 25 (BR).

Figure 3. Field photographs. A. The discoverer of the new species Jacques Kilela Mwanasomwe collecting a specimen at the thermal spring. B. Part of the population of C. kilelai existing of scattered tussocks on salty wed mud. C. Detail of a tussock of C. kilelai. Photographs: A by Diedo Mutombo Ngoy, B – C by Jacques Kilela Mwanasomwe.