Mesosetum canastrense R.C. Oliveira & M.W.S. Sousa, 2019

Mesosetum canastrense R.C. Oliveira & M.W.S. Sousa View in CoL , sp. nov.

Type:— BRAZIL. Minas Gerais: São Roque de Minas, Serra da Canastra National Park, near “curral de pedras” , 20°13’16.58”S, 46°27’54.55”W, 1440 m, 24 September 2017, C.Z. Fieker, M.G. Reis & I.L.D. Cunha 283 (holotype UB! GoogleMaps , isotypes BAA! GoogleMaps , CEN! GoogleMaps , HUFU! GoogleMaps , K! GoogleMaps , MO! GoogleMaps , P! GoogleMaps , RB! GoogleMaps , SPSC! GoogleMaps ). ( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 , 3A ‒ C View FIGURE 3 )

Diagnosis:— Similar to Mesosetum alatum , but differing mainly by the continuous line of trichomes at the collar (vs. absent or interrupted), synflorescences 6 ‒ 9(‒ 12) cm long (vs. 2.2 ‒ 3.2(‒ 7.5) cm long), pedicels with a truncate apex (vs. oblique), spikelets with the base surrounded by long appressed trichomes (vs. glabrous or with short sparse trichomes) and with an inconspicuous callus (vs. conspicuous and geniculate), and the lower anthecium neuter (vs. staminate or neuter).

Description:— Perennial, caespitose, short rhizomatous. Culms 60–80 cm tall, erect, many-noded, branching more toward the upper nodes; nodes pubescent, with short white trichomes. Leaves mostly cauline; leaf sheaths shorter than the internodes, the young ones pilose on the margins, the trichomes longer at the distal end, the old ones glabrous; collar with a continuous line of trichomes; ligules 0.25 ‒ 0.5 mm long, ciliate; leaf blades 5 ‒ 10 × 0.1 ‒ 0.2 cm, subulate, folded, the base slightly wider than the sheath, apex acuminate, glabrous on both surfaces, margins slightly scabrous. Peduncle 3 ‒ 7.5 cm long, terete, glabrous. Synflorescence composed of a single raceme, 6 ‒ 9(‒ 12) cm long, main axis ending in a spikelet; rachis winged, 2–4 mm wide, glabrous, with anastomosed nerves. Pedicels minute, ca. 0.5 mm long, glabrous, apex truncate. Spikelets solitary, 4 ‒ 5.1 × 1.5 ‒ 2 mm, imbricate in 2 series, laterally compressed, the base surrounded by long appressed trichomes 0.8 ‒ 1.2 mm long, callus inconspicuous; lower glume 3.6 ‒ 5.1 × 0.5 ‒ 1(‒ 1.5) mm, navicular, 3-nerved, nerves anastomosed at the upper portion, the central nerve generally with few and small trichomes on the dorsal surface, the trichomes up to 0.3 mm long, margins glabrous, muticous or with a mucro up to 0.5 mm long; upper glume 4 ‒ 4.5 × 0.8 ‒ 1.3 mm, 3-nerved, nerves anastomosed at the upper portion, margins ciliate at base, glabrous above, muticous; lower anthecium neuter; lower lemma 4 ‒ 5.1 × 1.4 ‒ 1.9 mm, 3-nerved, membranous, hyaline in the center, with two silky-pilose tufts on the margins in the middle portion; lower palea absent; upper anthecium bisexual, 3.8 ‒ 4.3 × 0.7 ‒ 1.2 mm wide, narrowly ellipsoid, paleaceous, acuminate; lodicules 2, minute; stamens 3, anthers ca. 2 mm long; caryopsis not seen.

Etymology:— The specific epithet highlights the only known area of occurrence of the new species: Serra da Canastra , in the Brazilian state of Minas Gerais.

Phenology:— Flowering specimens were collected in March and September.

Distribution and habitat:— The new species is only known from Serra da Canastra National Park, Minas Gerais, Brazil, where it is frequent in “campo limpo” vegetation of open Cerrado ( Figs. 2 View FIGURE 2 , 4 View FIGURE 4 ).

Conservation status:— Mesosetum canastrense has a restricted distribution and its calculated extent of occurrence (EOO) and area of occupancy (AOO), using the GeoCAT tool ( Bachman et al. 2011), were 1.1 km ² and 12 km ², respectively. No information was obtained to assess population trends. Frequent unnatural burnings are a possible threat to the species, although it occurs within a National Park. Following the guidelines for using the IUCN Red List Categories and Criteria ( IUCN 2017), M. canastrense fits in Data Deficient (DD), because the obtained data are insufficient to determine a threat category.

Additional specimens examined (paratypes):— BRAZIL. Minas Gerais: São Roque de Minas, Serra da Canastra National Park, near the historical source of the São Francisco River , 20°14’37.51”S, 46°26’50.38”W, 1361 m, 31 March 2016, C.Z. Fieker & M.G. Reis 173 ( HUFU, SPSC) GoogleMaps ; 20°14’47.99”S, 46°26’12.72”W, 1422 m, 23 September 2017, C.Z. Fieker et al. 271 ( HUFU, SPSC, UB) GoogleMaps .

Taxonomic notes: —The new species is morphologically similar to Mesosetum alatum due to the broadly winged rachis (2–4 mm wide and covering almost entirely the spikelets) and the absence of the tuft of trichomes on the back of the upper glume. Mesosetum alatum has leaves without a line of trichomes at the collar or with an interrupted one, an oblique pedicel apex, spikelets usually glabrous at the base with a characteristic geniculate callus, and the lower flower present or absent, when present staminate. On the other hand, Mesosetum canastrense has leaves with a continuous line of trichomes at the collar, a truncate pedicel apex, spikelets bearded at the base, the trichomes 0.8 ‒ 1.2 mm long, with an inconspicuous callus, not geniculate, and the lower flower absent (see Table 1 View TABLE 1 and Fig. 3 View FIGURE 3 ). Additionally, the two species also differ in geographical distribution, since M. alatum only occurs in the Brazilian state of Mato Grosso, and M. canastrense in Serra da Canasta in the state of Minas Gerais ( Fig. 4 View FIGURE 4 ).

According to Filgueiras (1989) and Silva (2017), the spikelet of M. alatum is 3.2 ‒ 4.2 mm long and the awn of the lower glume is 1.5–3 and 2.5–3.5 mm long, respectively. However, spikelets of M. alatum up to 5 mm long and with undeveloped awns were observed by us during the preparation of this work (for example, in the specimen: BRAZIL. Mato Grosso: Nova Nazaré, road from Nova Nazaré to Canarana, 1 August 2015, J.E.Q. Faria et al. 4947, UB). Therefore, due to overlapping measurements, the length of the spikelets and of the awns is not a good character to distinguish the new species from M. alatum .

The new species apparently does not have stolons. However, Ribeiro (2013) showed for related species that the stolons appear only in some phases of the cycle of the plants. As we could not observe M. canastrense in all phases, we chose not to include this character in the description. Additionally, it is quite intriguing that not even a single caryopsis was found in the plants of M. canastrense examined, even in mature inflorescences. Nevertheless, large apparently healthy populations of this species were observed in the field. Absence of fruits in several Cerrado grasses is not uncommon, including Mesosetum species ( Filgueiras 1989, Ribeiro 2013). Mesosetum canastrense therefore seems to belong to this group of native grasses that rarely or never produce fruits. Further investigation on the reproduction of this species is needed.