﻿Gymnostachyumcalcicola (Acanthaceae), a new species from limestone karst of Peninsular Malaysia

﻿Abstract A new species, Gymnostachyumcalcicola Rafidah, sp. nov. (Acanthaceae) is described from limestone karst in Peninsular Malaysia. Characters distinguishing it from related species, colour photographs, botanical illustration and provisional conservation status are provided.

The discovery of this distinctive new species is part of the comprehensive survey of the Peninsular Malaysia limestone flora in 2017.The species was found on the limestone hills in Federal Land and Development Authority (FELDA) Chiku and Perasu in Kelantan, and is endemic in Kelantan.The species inhabits partially shaded areas, and roots in cracks with thin soil layer on rocks at the base to the summit of karst limestone.After carefully examining the herbarium specimens and living material and reviewing the relevant literature, here we concluded that the newly discovered plants represented an undescribed species.Herewith, the new species is described and illustrated in detail.

Materials and methods
Measurements and morphological character assessments of the new species were undertaken and described using specimens collected from their natural habitat and living materials grown in the Forest Research Institute Malaysia (FRIM) Biodiversity Nursery.Photographs of the habit and all parts of the plants were made and botanical line drawings of floral and fruiting parts were prepared.Materials collected were deposited at the herbarium of Forest Research Institute Malaysia (KEP) and the flowers were preserved into the spirit collection in Copenhagen mixture.The available Gymnostachyum specimens from other herbaria such as BK, BKF, CAL, KLU, SING, UKMB and PSU were examined (herbarium acronyms follow Thiers 2024, continuously updated).In addition, images of the type specimens of Gymnostachyum were obtained from JSTOR Global Plants (http://plants.jstor.org)and Tropicos (http://www.tropicos.org).The provisional conservation assessment is based on the IUCN Red List Categories and Criteria Version 3.1 (IUCN 2012) and guidelines of the IUCN (2022).

Taxonomic treatment
Gymnostachyum calcicola Rafidah, sp.nov.urn:lsid:ipni.org:names:77342878-1Figs 1-3 Diagnosis.Unique among Peninsular Malaysian species of Gymnostachyum by having a racemose inflorescences occasionally lower axils with pairs of flowers and dichasium inflorescence with opposite branches.Gymnostachyum calcicola shows affinity with Gymnostachyum decurrens var.decurrens and var.robinsonii by its crowded rosette leaves at the base, however it is different in the inflorescences type.
Distribution and habitat.Endemic to Kelantan, Peninsular Malaysia; known only from limestone hills.Species grows in small populations, always observed in shaded areas, rooting in cracks on thin soil on limestone rocks, almost to the summit of the hill.
Etymology.The specific epithet refers to the limestone habitat of this species.Provisional IUCN regional conservation status.Endangered B2 ab(i,ii,iii).Most Chiku limestone hills were visited, but only two to three hills were home to this new species.A part of Chiku limestone hills is scheduled for quarries.The survival of the species remains uncertain.The species also has been recorded in Perasu limestone hills, about 40 km away from Chiku hills.Parts of FELDA Perasu limestone have been quarried, and surrounding areas are currently disturbed by the road constructions.All hills lie outside the network of Protected Areas.Notes.Ridley (1923) divided the Peninsular Malaysian species into two groups: (i) dwarf plants with single flower of long inflorescences and; (ii) shrubby plants with elongate stem.This new species falls into the first group (Table 1) together with Gymnostachyum decurrens Stapf var.decurrens

Map 1 .
Map of the Peninsular Malaysia indicating the location of Gymnostachyum calcicola in Peninsular Malaysia.

Figure 1 .
Figure 1.Gymnostachyum calcicola Rafidah A habit B flower (side view) C flower (front view) D portion of inflorescence showing dichasial cymose branches E portion of infructescence.

Figure 2 .
Figure 2. Gymnostachyum calcicola Rafidah A flowering plant B portion of inflorescence with flowers C flower D flower with opened corolla E bract, calyx and carpel with corolla and stamens removed F indumentum of anther along longitudinal line of dehiscence G anthers (dorsal and ventral views) H seeds I fruit J-K attachment of seeds (all drawn by Mohd Aidil Nordin).

Table 1 .
Comparison of Peninsular Malaysia species in Gymnostachyum in Group 1. Gymnostachyum ceylanicum absolutely indistinguishable from Sri Lanka specimen from the corolla colour.andvar.robinsonii(Ridl.)J.B.Imlay, G. diversifolium C.B.Clarke, G. pallens C.B.Clarke, G. kanthanense, and doubtful species recorded for Peninsular Malaysia, G. ceylanicum Arn.& Nees.The new species shows affinity with Gymnostachyum decurrens var.decurrens and var.robinsonii by its crowded rosette leaves at the base and its racemose and spicate inflorescences and G. pallens from its branched peduncle.It differs from the other species by not having a winged petiole and in having racemose inflorescences, occasionally lower axils with pairs of flowers and dichasium inflorescence with opposite branches. *