Axonopus graniticola, a new species of A. ser. Suffulti (Poaceae, Panicoideae, Paspaleae) from Minas Gerais, Brazil

Abstract A new species of Axonopus ser. Suffulti from Minas Gerais, Brazil, is described and illustrated. Comparison with morphologically related species, as well as comments on the ecology and the conservation status are provided.


Introduction
Axonopus P.Beauv. is an American genus of Poaceae comprising approximately 110 species (Black 1963, Clayton and Renvoize 1986, Cialdella et al. 2006). Most of its species occur in the tropics, where it is especially diverse in the Neotropical savannas, such as the Brazilian cerrado (Mendonça et al. 1998), the Espinhaço Range mountains (Viana and Filgueiras 2008), the Amazonian savannas and the Guayana Shield (Davidse et al. 2004). Traditionally, Axonopus was included in a wide circumscription of the tribe Paniceae, Panicoideae subfamily (e.g. Black 1963, GPWG 2001, Cialdella et al. 2006, Giraldo-Cañas 2007, 2008. However, the identity of Paniceae s.l. was challenged in the latest proposal of classifi cation of this tribe , based on an integrated analysis of ndhF plastid DNA and morphology. Th e authors split Paniceae s.l. into Paniceae s.s. (pantropical, basic chromosome number × = 10) and Paspaleae (American, × = 9), the latter encompassing Axonopus and other 38 genera. Chase (1911) recognized three sections of Axonopus : A . sect. Cabrera (Lag.) Chase, A . sect. Lappagopsis (Steud.) Chase, and A . sect. Axonopus , a circumscription that was followed by Dedecca (1956) in his revision of the genus for Brazil. Th ereafter, Black (1963), in his taxonomic study of the genus, divided A . sect. Axonopus into the series Axonopus , Barbigeri , Cappilares , Fastigiati , and Suff ulti, based on such combination of characters as life span, indumentum, the number of nerves in the upper glume, trichomes in the rachis of racemes, and the color of fertile fl orets. Th e only attempt to assess the monophyly of Black's Axonopus infrageneric groups using a combined analysis of morphological and molecular data (López and Morrone 2012) do not support Black's classifi cation. Some groups, however, appear to be monophyletic, like serie Suff ulti . Nonetheless, a comprehensive phylogeny including a broader sampling within Axonopus is necessary to support a robust infrageneric classifi cation of the genus.
Species of the Axonopus ser. Suff ulti are perennial plants, with the upper glume and lower lemma lacking a central nerve, and fertile fl orets characteristically shiny brown to dark brown (Black 1963, Cialdella et al. 2006. Cialdella et al. (2006) published a comprehensive revision of the taxon, providing detailed descriptions of the 16 accepted names, ornamentation of the upper fl oret on SEM, illustrations, a key for identifi cation of the species, and nomenclatural updates. Fifty fi ve species of Axonopus are currently indicated to Brazil (Filgueiras and Rodrigues 2012), and seven of them are placed in the Axonopus ser. Suff ulti .
A fl oristic survey in an overlooked granitic outcrop, or inselberg , in northeastern Minas Gerais, Brazil (de Paula et al. in prep.), revealed at least fi ve new species of fl owering plants. One of those, belonging to the Axonopus ser. Suff ulti , is herein presented, illustrated and compared with putatively related species. SEM images of the fertile fl oret, as well as comments on its ecology and the conservation status are provided. For SEM images, samples were mounted on stubs, coated with gold palladium in a Hummer 6.2 (Anatech, Union City, CA, USA) sputtering system and viewed with a JSM-541OLV (JEOL, Tokyo, Japan) at 10kV.
Morphological comments. Th e new species has perennial habit, scabrous pubescent rachis, with few scattered trichomes 0.8-1.5 mm long associated with the region of the pedicel insertion, the 2-4(-5)-nerved upper glume and 2(-3)-nerved lower lemma, and typically shiny brown and stiff fertile fl orets. In accordance with Black's (1963) infrageneric circumscription of Axonopus , accepted by Cialdella et al. (2006) and Giraldo-Cañas (2007, 2008, and the combination of the above features, Axonopus graniticola should be placed into the Axonopus subg. Axonopus ser. Suff ulti . A mid-nerve in the upper glume and lower lemma is found in some spikelets of the specimen de Paula 237 . Although this feature is uncommon in Axonopus ser. Suffulti (Cialdella et al. 2006), some species included in this group can bear a discrete mid-nerve in these bracts in some spikelets. For example, in the delicate Peruvian Axonopus elegantulus (J. Presl) Hitchc. and in A. fl abeliformis Swallen, from northern South America, some spikelets can have the upper glume with a visible mid-nerve; in the Venezuelan Axonopus magallanesiae Giraldo-Cañas, both upper glume and lower lemma can be 4-5-nerved, with a noticeable mid-nerve on the bracts (Cialdella et al. 2006), as recorded in some spikelets of the new species.
Axonopus fl abeliformis shares with A. graniticola the characteristically equitant base, with distichous, laterally compressed and persistent leaf sheaths, disposed along the culm. Th e compound panicle, occasionally occurring in A. fl abeliformis , and spikelets 1.6-2.2 mm long, also suggest affi nity, even though superfi cial, to the new species. Axonopus graniticola can be easily distinguished from A. fl abeliformis by its wider leaf blades (1.5-2.5 cm vs. 0.5-0.9 cm in A. fl abeliformis ), the rounded and subcordate base of the blade arising from a constriction in the ligular region (against blade bases straight and following the sheath apex width in A. fl abeliformis ), and its multi-fl owered panicles (26-75 racemes vs. 6-20(-30) racemes in A. fl abeliformis ).
Th e new species also bears slight resemblance to Axonopus pressus (Nees ex Steud.) Parodi, from the Brazilian cerrado , Bolivia and Paraguay, by its strongly conduplicate and keeled leaf sheaths, giving the typical laterally compressed aspect to the plant. However, the leaves of A. pressus are predominantly basal, contrasting with mostly caulinar leaves of A. graniticola , with shorter spikelets (1.8-2 mm long, vs. 2.2-3 mm in A. pressus ), wider leaf blades (1.5-2.5 cm, vs. 0.8-1.2 cm in A. pressus ) and infl orescences with 26-75 racemes (against less than 35 racemes in A. pressus ). Moreover, the panicles of the new species are compound, with the lower branches re-branching in 5-18 racemes, a feature absent in A. pressus , with its panicles with unbranched racemes.
Th e fl at and characteristically wide leaf blades and the compound panicles of the new species bear a slight resemblance to the widely distributed Axonopus scoparius (Flüggé) Kuhlm . However, the latter species is placed in the Axonopus sect. Axonopus ser. Barbigeri Black (Black 1963, Giraldo-Cañas 2007, 2008, and is characterized, among others, by spikelets with the upper glume and lower lemma with a central nerve, and pale brown upper fl orets. Axonopus graniticola plainly fi ts the circumscription of the Axonopus sect. Axonopus ser. Suff ulti, as discussed above. Ornamentation of fertile fl oret on SEM. (Figure 2). Abaxial surface of palea and lemma ornamented with papillae, silica bodies, macro-hairs and micro-hairs. Papillae simple, conical, apex acute, one per cell, evenly distributed in longitudinal rows on the fl oret surface, except in the margins of the lemma, which lack papillae. Silica bodies equidimensional, dumbbell shaped, visible on the apical portion of lemma margins. Macro-hairs unicellular, simple, located in the apex of lemma and palea and in the basal portion of the lemma (Figure 2 E). Micro-hairs collapsed in the studied material, probably due to samples preparation process, distributed in the apex of lemma and palea and in the basal portion of the lemma.
Th e presence of numerous papillae, dumbbell shaped equidimensional silica bodies on the apex of fertile fl oret and macro-and micro-hairs on the base and apex of fl oret are typical features of species included in Axonopus ser. Suff ulti (Cialdella et al. 2006). Although no unique diagnostic feature was recorded in Axonopus graniticola , papillae with acute apex seems to be uncommon among species of A. ser. Suff ulti , being only recorded in the new species and in A. polydactylus (Steud.) Dedecca, A. ramosus Swallen and A. suff ultus (Mikan ex Trin.) Parodi (Cialdella et al. 2006).
Distribution and ecology. Th e new species is known only from its type locality, an inselberg in the municipality of Teófi lo Otoni, eastern Minas Gerais, Brazil. It occurs on granitic and gneissic rock outcrops, surrounded by the Atlantic Forest matrix (Veloso et al. 1991), at elevations around 600 m.
Th e species is found in depressions fi lled with thin soil, forming dense clumps, surrounded by rocky surface. During the rainy season, the profuse growth of new leaves with conspicuous fl at and wide blades gives a vivid green color to the clumps ( Figure  3A), in contrast with the pale brown, almost bladeless, clumps observed during the dry season ( Figure 3C). Th e persistent leaf sheaths covering the culms and the readily deciduous leaf blades may be adaptations to avoid desiccation during the dry season and serve as protection against high temperatures of this extremely seasonal environment. Th ese features are described for other species among monocots families, like Velloziaceae and Cyperaceae, which are usually known as desiccation-tolerant pla nts (Porembski 2007, Porembski andBarthlott 2000).
Th e vegetation of the inselberg is infl uenced by the soil (Porembski et al. 1998, Porembski 2007, and its fl ora is predominantly xeromorphic. Adaptations to drought and high insolation are common for the species from the type locality of Axonopus graniticola . Desiccation tolerance is found in other plant groups that occur in this area, as in some ferns and allies ( Sellaginella convoluta (Arn.) Spring, S. sellowii Hieron., Conservation. Th e species is known so far from a single granite-gneiss outcrop in the Teófi lo Otoni region, Minas Gerais, Brazil. Due to the poor state of knowledge of the fl ora from that region (Martinelli 2007), more fi eld eff orts are required to clarify the distributional range of this species. In accordance with the IUCN (2001) guidelines, the species should be evaluated as Data Defi cient.
Although it was not possible to assess the precise conservation status of the species, it is important to note that the vegetation of the inselbergs are under threat due to the ever increasing granite and gem exploration, road-building, grazing and illegal plant collection in southeastern Brazil's inselbergs (Saff ord and Martinelli 2000). To fi ll the gap of information in this diverse and poorly studied area, and therefore provide guidelines for the conservation of the fl ora in the region, taking into account that rock outcrops support a large number of endemics (Porembski 2007), a broader study of the fl ora of the Teófi lo Otoni inselbergs is urgently needed.