Thursday, February 25, 2021

[Botany • 2019] Dictyanthus stevensii (Apocynaceae; Asclepiadoideae; Gonolobinae) • A New Species from Chimalapas Region, Oaxaca, Mexico

Dictyanthus stevensii Gonz.-Martínez, Lozada-Pérez et L.O. Alvarado 

in González-Martínez, Lozada-Pérez & Alvarado-Cárdenas, 2019.
(Illustrated by César Adrián González Martínez). 

A new species of the genus Dictyanthus is herein described and illustrated, more than 30 years since the last paper describing new species of this genus. Dictyanthus stevensii sp. nov. is known only from the Zoque forest in the Chimalapas region in the state of Oaxaca, Mexico. This species differs from all other species because it has the smallest flowers within the genus. It is morphologically related to D. eximius, a microendemic species of Chiapas. Information on the distribution and habitat of this new species is given, and its conservation status is proposed as Critically Endangered B2ab(ii). An identification key to Dictyanthus species in southern and southerneast Mexico is also provided.

Keywords: conservation, endemic, Matelea, taxonomy, Zoque forest, Eudicots

Holotype of Dictyanthus stevensii.
A. Herbarium specimen showing the inflorescences in monochasia and the size of flowers; bar 4 cm; B. Base of the blade abaxially, with three colleters and petiole with mixed indumentum of short straight trichomes and uncinated trichomes; C. Flower. The parallel vertical venation can be observed in the tube of the corolla; bar 2.5 mm; D. Corolla with concentric venation in the limb and reticulated towards the lobes with short straight trichomes on the veins; showing the gynostegium. The corpusculum and the apex of one lobe of the corona are shown exerting the corolla tube; bar 2.5 mm.

Dictyanthus stevensii.
A. Habit of the plant with inflorescences; B. Flower; C. Corona and gynostegium; D. Pollinarium.
A‒D based on salomón Maya J. 3463 (MEXU) 
(Illustrated by César Adrián González Martínez). 

Morphological comparison of the flower of some species of Dictyanthus related to Dictyanthus stevensii, based on herbarium specimens.
A. D. hamatus, Diego 6672 (FCME); B. D. eximius, stevens 26651 (MEXU);
C. D. tuberosus, Pringle 4482 (MEXU); E. Dictyanthus stevensii, salomón Maya J. 3463 (MEXU);
bar = 1 cm. 

Dictyanthus stevensii Gonz.-Martínez, Lozada-Pérez et L.O. Alvarado sp. nov. 

Dictyanthus stevensii is morphologically related to D. eximius (Stevens 1988: 1552) Stevens (2000: 243) but differs by having a row of uncinated and interpetiolar trichomes, the indumentum of young stems consists of uncinated and straight trichomes only, corolla green with undulate margin, the lobes of the corona are oblong with spatulate, rounded apex or slightly bilobulated, the apex is exerted from the corolla tube and with the anthers vertices slightly exerted.

Etymology:— The specific epithet honors Dr. Warren Douglas Stevens (b. 1944), botanist, collector and investigator at the Missouri Botanical Garden. Stevens has greatly contributed to the knowledge and taxonomy of the subfamily Asclepiadoidae. Among his contributions, his participation as editor in chief of the Flora of Nicaragua is one of the most important. He has also described over 130 new species from many genera of Asclepiadoideae and other families, mostly from Mexico and Central America. He carried out the most exhaustive taxonomic revision of Dictyanthus (Stevens 1975, 1988) and recognized it as an independent genus from Matalea s.l., based on morphological evidence (Stevens 1999, 2000). In addition, he described six new species for the genus and provided new information about this genus in the Mexican Flora (Stevens 1988).

César Adrián González-Martínez, Lucio Lozada-Pérez and Leonardo O. Alvarado-Cárdenas. 2019. Dictyanthus stevensii (Apocynaceae; Asclepiadoideae; Gonolobinae), A New Species from Chimalapas Region, Oaxaca, Mexico. Phytotaxa. 394(1):79-88. DOI: 10.11646/phytotaxa.394.1.5