Research Article |
Corresponding author: Daniel A. Zhigila ( danielandrawus.zhigila@uct.ac.za ) Academic editor: Marcos A. Caraballo-Ortiz
© 2022 Daniel A. Zhigila, A. Muthama Muasya.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Zhigila DA, Muasya AM (2022) Thesium muasyae (Santalaceae), a new species from the limestone fynbos of the Overberg, South Africa. PhytoKeys 201: 1-14. https://doi.org/10.3897/phytokeys.201.80774
|
Thesium muasyae, a new species of the family Santalaceae, is described and illustrated. This species has unique morphological and ecological characters, differentiating it from other closely related species of the genus, such as T. karooicum. These characters include plants forming compact shrubs to about 30 cm tall with glabrous surfaces; leaves recurved, to about 4 cm long, terete to triangular, apiculate; flowers placed in lax spikes or borne solitary; and style up to about 2.5 mm long. Ecologically, T. muasyae is endemic to the limestone fynbos in the Overberg, Bredasdorp District, South Africa. Molecular phylogenetic evidence places this species in Subgenus Frisea Section Barbata, as closest sister to T. hispidulum + T. karooicum. A preliminary conservation Red List assessment suggests that T. muasyae is Critically Endangered, based on its population size, area of occupancy and extent of occurrence.
Endemic, Greater Cape Floristic Region, systematics, taxonomy, Thesiaceae
Thesium L. is the largest genus in the family Santalaceae with > 360 species (
Recent molecular phylogenetic analyses for Santalaceae, with robust taxa and loci sampling of Thesium, supported a monophyletic genus (
Eleven species are currently recorded in the limestone fynbos and renosterveld of the Overberg region, South Africa (
The morphological assessments of the new species were carried out on our field collections and on herbarium specimens deposited at BOL, NBG (including SAM and STE vouchers) and PRE (codes as indicated by
Whole genome DNA was extracted from the silica-gel dried leaf materials collected during our fieldworks between 2019 and 2021. The extraction was performed using a modified CTAB protocol (
Forward and reverse reaction sequences were assembled using Chromaspro version 2.1.5 (
A model-based Bayesian method (MrBayes) was used for the phylogenetic analyses on XSEDE v.3.2.6 (
The preliminary conservation Red List status for the species was determined using the IUCN guidelines (
South Africa. Western Cape Province, Bredasdorp District, on limestone ridges, south east of Vanderstelskraal Farm, Overberg, 34°24'53.2"S, 20°15'10.5"E [34.41478°S, 20.25292°E]; elev. 60 m; 21 October 2021, D.A. Zhigila & A.M. Muasya 1308 (holotype, BOL; isotypes: K, NBG, PRE).
Thesium muasyae is morphologically similar to T. karooicum
Main differentiating morphological features of Thesium muasyae from its most-similar congeners.
T. muasyae | T. karooicum | T. sondarianum | T. hispidulum | |
---|---|---|---|---|
Plant height | 10–30 cm | 10–70 cm | 50–100 cm | 10–50 cm |
Branching pattern | sympodial to intricate | divaricate | dichotomous | decumbent |
Plant surface | Glabrous | minutely pubescent | minutely pubescent | pubescent |
Leaf curvature | recurved or straight | recurved | recurved | recurved or straight |
Leaf margin | Terete | scabrous | scabrous | scabrous |
Leaf apex | Apiculate | acuminate | acutely mucronate | acuminate |
Inflorescent type | elongated lax or solitary spikes | globose spikes | globose spike | globose spikes |
External glands | present | present | absent | absent |
Style length | 1–2.5 mm | 0.5–1.5 mm | 1–2.5 mm | 0.3–0.4 mm |
Style | above anther | below anther | below anther | below anther |
Anther | exserted | exserted | partly exserted | inserted |
Post-staminal trichomes | attached to anthers | free from anthers | attached to anthers | attached to anthers |
Fruit length | 4–7 mm | 4–10 mm | 5–10 mm | 3–4 mm |
Fruit ribs | 5-ribbed | 10-ribbed | 5-ribbed | 10-ribbed |
Substrate | limestone slopes | sandstone and shale | sandstone | sandstone and shale |
Biome | Limestone Fynbos | Succulent Karoo | Grassland | Sandstone Fynbos |
A perennial shrub, arising from woody rootstock, glabrous, to about 30 cm tall. Stems woody, erect to suberect, much branched, 3.0–5.0 mm in diameter, deeply grooved longitudinally. Branches 10–20 in number, mainly from the base, scarcely grooved, angled from > 45° to < 90°, branching pattern intricate to sympodial. Leaves terete to triangular, somewhat succulent, adpressed to the branchlets, lanceolate or oblanceolate or somewhat triangular, 1.5–3 × 0.5–1.5 cm, basally decurrent, midrib inconspicuous, not keeled but recurved, margins not distinct or entire, apically apiculate. Inflorescences a lax terminal spike or flowers solitary in leaf and bract axils. Bracts 2–4, leaf-like, slightly adnate to the base of peduncle, linear to lanceolate, 1.0–2.0 × 0.3–0.5 mm, margin entire, apex acute to acuminate, green; bracteoles bract-like, but smaller, adpressed to the pedicel, shorter than flower length. Flowers patelliform, on short peduncles, 5-merous, 2.0–5.5 × 1.5–5.0 mm, perianth lobe segments lanceolate, external gland conspicuously elongated between perianth lobe segments, 2.0–2.5 × 1.0–1.2 mm, lobe apex uncinate, obtuse, incurved, perianth lobe apical trichomes present, lobe margins entire, lobe internal colour white, external colour greenish black; hypanthium clearly marked, to about 0.5 mm long, hypanthium length longer than perianth lobe tube and wider. Stamens equal flower merosity, 0.2–0.3 mm long, staminal filaments exserted slightly above stigmas, attached to the perianth lobe walls by a tuft of trichomes, downwardly-directed basal trichomes absent. Style together with stigma 4–6 mm long; placental column twisted. Fruits subglobose to oblong, ovary portion oval, 5.0–8.0 × 4.5–5.5 mm, green to creamy green, glabrous with 10 conspicuous longitudinal ribs, reticulate veins prominent, pedicels enlarging into elaiosomes, persistent perianth segments equal to longer than the fruit.
Morphological features of Thesium muasyae A whole plant in habitat B type material D.A. Zhigila & A.M. Muasya 1308 C branchlet and leaves D fruiting branchlet E fruit lateral view F inflorescences and leaves G flower longitudinal section showing long style in relation to anthers and twisted placental column H flower subtended by bracts I elaiosome on fruit. Photographs by Daniel A. Zhigila. Scale bars: 0.5 mm.
Thesium muasyae was collected on the limestone ridges, south east of Vanderstelskraal Farm, Overberg, Bredasdorp District, Western Cape Province, South Africa (Fig.
Map of A South Africa with the red outline indicating the Greater Cape Floristic Region (GCFR) B the GCFR showing the type locality (red solid circle) of Thesium muasyae and of the congener species, T. hispidulum (aqua solid stars), T. karooicum (blue solid triangles) and T. sonderianum (fuchsia solid squares).
The collections were made in October with fruits and few flowers. Based on the average of 40 days from flowering to fruiting stage in Thesium species (pers. obs.), we can then extrapolate the flowering period to be between August and November.
The specific epithet ‘muasyae’ honors Professor A. Muthama Muasya for his immense contribution to the floristics and taxonomy of the Overberg and Cape plant species.
We estimated a total of 10–20 individuals of T. muasyae in a single population over an extent of 0.0 km2 and the area of occupancy of about 5.0 km2. Although this species is on a private farm, grazing from livestock is an immediate threat. In addition, the entire Overberg Renosterveld habitat is considered as Endangered due to intense agricultural activities and the areas being fire-prone (
South Africa. Western Cape Province, Bredasdorp District, on limestone ridge, south east of the Vanderstelskraal Farm, 34°24'52.1"S, 20°15'8.1"E [34.41447°S, 20.25225°E], elev. 63 m, 21 October 2021, D.A Zhigila & A.M Muasya 1312 (BOL!); 34°24'53.2"S, 20°15'10.5"E [34.41478°S, 20.25292°E], elev. 65 m, A.M Muasya & D.A Zhigila 8276 (BOL).
The Maximum Parsimony and Bayesian analyses placed T. muasyae (red bold on Fig.
A 50% majority-rule consensus tree for Santalaceae that include the new species Thesium muasyae (red bold) based on a combined nrITS and plastid trnL-F regions obtained from Bayesian Inference. Numbers on the nodes indicate clades with bootstrap and posterior probability support values of > 95% and 0.90 respectively.
The morphological characters suggest that T. muasyae fits into section Barbata (
In the last five years, nine new species and several new records of Thesium have been discovered from the Overberg Region (
We thank the Smuts Memorial Botanical Fellowship for a postdoctoral scholarship for the year 2021 offered to the first author. We thank the Gombe State University for permission to embark on the postdoctoral fellowship. The authors appreciate the International Association of Plant Taxonomists (IAPT) for the 2021 IAPT Research Grant given to the first author to support the molecular work. Additional financial support was received from the National Research Foundation (Foundational Biodiversity Information Programme, Grant 136337 to AMM). The permit to collect herbarium specimens was granted by the Western Cape Nature Conservation Board, permit number CN35-28-17379 – DAZ. We also thank the curators of BOL, NBG and PRE for access to Thesium specimens. Line drawing by Pia M. Eibes is much appreciated. We appreciate the anonymous reviewers and the editor, Marcos A. Caraballo-Ortiz, for important contributions which have tremendously improved this manuscript.
Suplementary tree
Data type: (phyl. file)
Explanation note: Tree files including sequences from previous studies.