Heteropterys rosmarinifolia, a new species of Malpighiaceae with verticillate leaves from savannas grasslands of central Brazil

Abstract A new species of Heteropterys belonging to the Parabanisteria informal group is described for the savannas grasslands of the Serra do Tombador Natural Reserve, municipality of Cavalcante, State of Goiás, Brazil. Heteropterys rosmarinifolia is easily distinguished from the remaining Brazilian species of the Parabanisteria informal group due to its stems unbranched, leaves associated with the inflorescence verticillate, blades linear to very narrowly oblong, strongly conduplicate, ascending to upright, and sparsely sericeous to glabrous at age. We present a complete morphological description for the new species, photographic plates, comments on its distribution, ecology, and taxonomy, besides an identification key to the species of Heteropterys from the Parabanisteria group from the State of Goiás, Brazil.


Introduction
Heteropterys Kunth is the largest genus of Neotropical Malpighiaceae, with ca. 160 species occurring in various open to closed habitats from northern Mexico to northern Argentina (Anderson et al. 2006;POWO 2021). A single species, H. leona (Cav.) L., is also widely and naturally distributed in western Africa (Anderson 2001). The genus includes a great deal of morphological variation in life forms (i.e., subshrubs, shrubs, lianas to small trees), gland position on the leaves (i.e., glands inserted at the base, middle or apex of petioles and/or along the leaf blade and/or on margins), inflorescence architecture (i.e., 1-flowered cincinni arranged in thyrsi, corymbs, or umbels), petal color (i.e., white, yellow, orange, pink, red to purple), petal shape when in bud (i.e., smooth or dorsally keeled), and shape of the style apex (i.e., rounded, truncate, uncinate, or hammer-shaped) (Amorim 2003;Pessoa et al. 2014;). The only morphological character shared by all species in the genus is the schizocarpic fruit with winged mericarps, in which the dorsal wing is more developed than the lateral ones, thickened on the inferior side, and curved towards the floral center . This peculiar character is unique in Malpighiaceae and currently the sole synapomorphy of the monophyletic Heteropterys (Almeida & van den Berg, 2021).
The immense morphological variation in Heteropterys makes it one of the most taxonomically complex genera in the family, with no modern revision (Almeida pers. observ.). Nonetheless, seven informal groups, derived from different taxonomic ranks proposed in the past, are currently recognized in the literature: Apytchia, Madarophyllis, Metallophyllis, Parabanisteria, Rhodopetalis, Stenophyllarion, and Xanthopetalis (Amorim 2003). Out of those, the Parabanisteria group is the most diversified, with over 50 species confined to Neotropical savannas from the Amazon domain (i.e., campinaranas), Central Brazil and Bolivia, and the llanos from Colombia and Venezuela (POWO 2021; Almeida pers. observ.). Species of Parabanisteria are easily recognized by their large flowers arranged in thyrsi and covered in brown hairs, the apex of sepals revolute at anthesis, petals bright yellow and usually widely elliptic, and lateral wings of mericarps usually absent .
During the preparation of the Heteropterys monograph for the Flora do Brasil 2020 project , we came across two recently collected specimens of Heteropterys belonging to the Parabanisteria group with unusual verticillate leaves from Serra do Tombador, municipality of Cavalcante, State of Goiás. We describe these specimens as a new species, presenting detailed morphological descriptions, photo plates, and comments on its distribution, ecology, and taxonomy.

Methods
Morphological data were based on herbaria samples (HUEFS, RB, and UFRN; acronyms according to Thiers, continuously updated). The indumentum terminology follows Anderson (1981), structure shapes follow Radford et al. (1974), inflorescence terminology and morphology follow Weberling (1965Weberling ( , 1989, and fruit terminology follows Spjut (1994) and Anderson (1981). The conservation status was proposed following the recommendations of IUCN Red List Categories and Criteria, Version 3.1 (IUCN 2012). GeoCAT (Bachman et al. 2011) was used for calculating the Extent of Occurrence (EOO) and the Area of Occurrence (AOO). Diagnosis. Heteropterys rosmarinifolia differs from the remaining Brazilian species of the Parabanisteria group due to its stems unbranched (vs. branched), leaves associated with the inflorescence verticillate (vs. opposite to subopposite), blades linear to very narrowly oblong (vs. several shapes, but never linear or narrowly oblong), strongly conduplicate (vs. plane), ascending to upright (vs. patent).
Conservation status. Heteropterys rosmarinifolia is known only from two collections, probably from the same population within the limits of the Serra do Tombador Natural Reserve in the State of Goiás, Brazil. Until additional fieldwork can be done in the savannas of northern Goiás, this species is best categorized as data deficient (DD).
Etymology. The epithet makes reference to the leaves of the new species that resemble those of the widely cultivated aromatic herb, rosemary (Salvia rosmarinus Spenn., Lamiaceae).
Notes. Heteropterys rosmarinifolia is easily distinguished from the remaining species of the Parabanisteria group by the vegetative characters presented in the abovementioned diagnosis. It is most similar to H. pannosa Griseb. due to its small stature, delicate branches, and narrow leaf-blades. However, it can be differentiated by its stems distally unbranched (vs. branched in the upper half in H. pannosa), leaf-blades linear to very narrowly oblong, strongly conduplicate, ascending to upright, and abaxially rusty-sericeous (vs. narrowly elliptic, conduplicate, patent, and abaxially greyish-lanate-tomentose), leaves associated with the inflorescence verticillate (vs. opposite to ternate), cincinni verticillate (vs. subopposite to opposite), and anthers glabrous with connectives white (vs. pubescent and brown). Despite fruits still being unknown for H. rosmarinifolia, they most likely are similar to the ones of H. pannosa, with the dorsal wing reduced to a crest, and nuts lacking lateral winglets (i.e., wingless nut). Alternatively, most species of the Parabanisteria group present a developed dorsal wing . Floral and fruit characters are highly conserved in the Parabanisteria group and have been traditionally considered of little taxonomic relevance (Niedenzu 1928). Consequently, this group's taxonomy currently heavily relies on vegetative characters related to life form, branch, and leaf morphology, rendering it the most taxonomic convoluted in Heteropterys (Niedenzu 1928;Almeida pers. observ.). Further studies are still necessary to properly explore the relevance of floral and fruit characters in this group and review species boundaries. For the time being, we provide below an identification key for the species of Heteropterys from the Parabanisteria group from the State of Goiás, Brazil.

Key to the species of the Parabanisteria group from Goiás
Modified from Pessoa et al. 2014.  H. procoriacea (Fig. 3G)