Axonopus graniticola P.L.Viana, 2013

Viana, Pedro Lage & Paula, Luiza Fonseca Amorim de, 2013, Axonopus graniticola, a new species of A. ser. Suffulti (Poaceae, Panicoideae, Paspaleae) from Minas Gerais, Brazil, PhytoKeys 21, pp. 7-16 : 8-12

Axonopus graniticola P.L.Viana sp. nov.

Diagnosis.

Axonopus graniticola is distinguished from all other species of the Axonopus ser. Suffulti by its mostly caulinar leaves, distichous laterally compressed leaf sheaths, 1.5-2.5 cm wide leaf blades, deciduous with a subcordate base, and multi-racemose inflorescences of 26-75 racemes, with the basal ones re-branched.

Type.

BRAZIL: Minas Gerais: Município Teófilo Otoni, Afloramento rochoso ao lado esquerdo da MG 418, cerca de 30 km norte de Teófilo Otoni, 17°51'21.5"S, 41°15'39.4"W, 560 m alt., 8 Jan 2011, L.F.A. de Paula, N.F.O. Mota, P.L. Viana, T.B. Jorge, P.M. Burkowski 145 (Holotype: BHCB! Isotypes: RB! NY!) ( Figures 1 -3 ).

Description.

Plants perennial, densely caespitose, with very short falciform rhizomes. Culms 95-125 cm long, erect to decumbent, slightly curved at the base, not geniculate, unbranched; nodes various, hidden by leaf sheaths, glabrous; internodes 5-8.5 mm wide, cylindrical to slightly flattened, glabrous, stramineous. Leaves distichous, mostly caulinar; leaf sheaths 5.5-32 cm long, larger than the internodes, conduplicate, strongly keeled, striate, scabrous, glabrescent, persistent; ligule 0.15-0,20 mm long or absent, ciliate, apparently deciduous, because it is usually absent in older leaves; collar prominent, glabrous; leaf blades (4.5)12-32 × 1.5-2.5 cm, oblong to linear, lanceolate, flat, retrosely scabrous abaxially, antrorselly scabrous adaxially, eventually with sparse hairs on abaxial or adaxial surfaces, deciduous, nerves prominent, margins scabrous, base rounded, subcordate, arising from a constriction of 1-2 mm long in each margin of the ligular region, apex obtuse, asymmetrical, emarginate, slightly folding, reflexed, scabrous. Inflorescences 2 per flowering culm, terminal and axillary; peduncle up to 55 cm long, partially included in the leaf sheaths, cylindrical to angulose, striate, scabrous; pulvinulus pubescent; main axis 8-16.5 × 0.05-0.14 cm, angulose, striate, scabrous; panicles 12-26 cm long, in dense clusters of alternate to verticillate racemes, the lower branches re-branching in 5-18 racemes; racemes (4 –)9– 16.5 cm long, the apical ones slightly shorter than the basal, 26-75 per panicle; rachis of racemes triquetous, fertile all along, except for the 1-4.5 mm basal portion length, ending in a fertile spikelet, (5)10-15 spikelets per portion of 25 mm long, pubescent, scabrous in the angles; pedicels 0.25-0.5 mm long, scaberulous, sometimes with a few hyaline tuberculate trichomes to 0.8-1.5 mm long. Spikelets 1.8-2.0 × 0.6-0.8 mm, oblong-ellipsoid, dorsiventrally compressed, apex acute; upper glume as long as the spikelet, elliptical, membranous, glabrous or with sparse trichomes, hyaline to stramineous, 2 –4(– 5)-nerved, nerves prominent, scaberulous in the apex, mid-nerve occasionally present; lower lemma glumiform, 2(-3)-nerved, nerves glabrous; upper lemma 1.8-2.0 × 0.8-0.9 mm, elliptical, stiff, glabrous, except for a discrete tuft of short white hairs at the apex, densely ornamented by diminute papillae, fading in den sity toward the margins, shiny brown to dark brown, apex acute, brown to pale, base brown to pale; upper palea similar to the upper lemma but slightly shorter, 1.7-1.9 × 0.6-0.8 mm, glabrous. Lodicules 0.2-0.3 mm long, 2, oblong, erose; stamens 3, anthers ca. 0.8 mm, dorsifixed, purplish; stigmas plumose, whitish. Caryopsis not seen.

Etymology.

The epithet refers to the occurrence of the plants of this species on exposed granite rock outcrops.

Morphological comments.

The 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 florets. 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. Suffulti .

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 Axonopus flabeliformis 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 flabeliformis shares with Axonopus graniticola the characteristically equitant base, with distichous, laterally compressed and persistent leaf sheaths, disposed along the culm. The compound panicle, occasionally occurring in Axonopus flabeliformis , and spikelets 1.6-2.2 mm long, also suggest affinity, even though superficial, to the new species. Axonopus graniticola can be easily distinguished from Axonopus flabeliformis by its wider leaf blades (1.5-2.5 cm vs. 0.5-0.9 cm in Axonopus flabeliformis ), 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 Axonopus flabeliformis ), and its multi-flowered panicles (26-75 racemes vs. 6 –20(– 30) racemes in Axonopus flabeliformis ).

The 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 Axonopus pressus are predominantly basal, contrasting with mostly caulinar leaves of Axonopus graniticola , with shorter spikelets (1.8-2 mm long, vs. 2.2-3 mm in Axonopus pressus ), wider leaf blades (1.5-2.5 cm, vs. 0.8-1.2 cm in Axonopus pressus ) and inflorescences with 26-75 racemes (against less than 35 racemes in Axonopus pressus ). Moreover, the panicles of the new species are compound, with the lower branches re-branching in 5-18 racemes, a feature absent in Axonopus pressus , with its panicles with unbranched racemes.

The flat 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 florets. Axonopus graniticola plainly fits the circumscription of the Axonopus sect. Axonopus ser. Suffulti , as discussed above.

Ornamentation of fertile floret 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 floret 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 2E ). 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.

The presence of numerous papillae, dumbbell shaped equidimensional silica bodies on the apex of fertile floret and macro- and micro-hairs on the base and apex of floret are typical features of species included in Axonopus ser. Suffulti ( 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 Axonopus ser. Suffulti , being only recorded in the new species and in Axonopus polydactylus (Steud.) Dedecca, Axonopus ramosus Swallen and Axonopus suffultus (Mikan ex Trin.) Parodi ( Cialdella et al. 2006).

Additional specimen examined (Paratype).

BRAZIL: Minas Gerais: Município Teófilo Otoni, Afloramento rochoso ao lado esquerdo da MG 418, cerca de 30 km norte de Teófilo Otoni, em inselbergue, 17°51'11"S, 41°15'44"W, 650 m alt., 16 Apr 2011, L.F.A. de Paula, M. Augsten 237 (BHCB, RB).

Distribution and ecology.

The new species is known only from its type locality, an inselberg in the municipality of Teófilo 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.

The species is found in depressions filled with thin soil, forming dense clumps, surrounded by rocky surface. During the rainy season, the profuse growth of new leaves with conspicuous flat 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 ). The 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. These features are described for other species among monocots families, like Velloziaceae and Cyperaceae , which are usually known as desiccation-tolerant plants ( Porembski 2007, Porembski and Barthlott 2000).

The vegetation of the inselberg is influenced by the soil ( Porembski et al. 1998, Porembski 2007), and its flora 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, Sellaginella sellowii Hieron., Cheilanthes geraniifolia (Weath.) R.M.Tryon & A.F.Tryon) and in Angiosperms, such as Cyperaceae ( Trilepis lhotzkiana (Nees) ex Arn.), and Velloziaceae ( Barbacenia spp., Vellozia spp.). Succulence occurs in Cactaceae ( Coleocephalocerus buxbaumianus Buining, Pilosocereus brasiliensis (Britton & Rose) Backeb.), Bromeliaceae ( Encholirium gracile L.B.Sm.), Orchidaceae ( Cyrtopodium glutiniferum Raddi, Encyclia spiritusanctensis L.C.Menezes), and in some Piperaceae ( Peperomia spp.). Leaf deciduousness is also an adaptation in Wunderlichia azulensis Maguire & G.M.Barroso ( Asteraceae ) and Tabebuia reticulata A.H.Gentry ( Bignoniaceae ).

Conservation.

The species is known so far from a single granite-gneiss outcrop in the Teófilo Otoni region, Minas Gerais, Brazil. Due to the poor state of knowledge of the flora from that region ( Martinelli 2007), more field efforts are required to clarify the distributional range of this species. In accordance with the IUCN (2001) guidelines, the species should be evaluated as Data Deficient.

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 ( Safford and Martinelli 2000). To fill the gap of information in this diverse and poorly studied area, and therefore provide guidelines for the conservation of the flora in the region, taking into account that rock outcrops support a large number of endemics ( Porembski 2007), a broader study of the flora of the Teófilo Otoni inselbergs is urgently needed.

Figures

Figure 1. Axonopus graniticola P. L. Viana A Habit B Ligular region, adaxial side C Rachis of receme D Spikelet, upper glume view E Spikelet, lower lemma view F Upper floret, lemma view G Upper floret, palea view. Drawn from the holotype (de Paula et al. 145).

Figure 2. SEM micrographs of upper floret A Lemma view B Palea view C Apical portion of floret showing silica bodies (arrows) D Upper lemma apex, showing conspicuous macrohairs and pappilae E Basal portion of floret. Images taken from the holotype (de Paula et al. 145).

Figure 3. In situ photographs of Axonopus graniticola P. L. Viana A Dense clump of A. graniticola during the rainy season B Flowering culm C Clumps, in the beginning of the dry season D Detail of panicle. Photographs by L. F. A. de Paula.