Homalolepis planaltina Devecchi & Pirani, 2018

Devecchi, Marcelo F., Thomas, William W. & Pirani, José R., 2018, Two new dwarf species of Homalolepis (Simaroubaceae) from the Brazilian Cerrado (Neotropical savanna), Phytotaxa 336 (3), pp. 252-262 : 253-257

Homalolepis planaltina Devecchi & Pirani , sp. nov. Figures 1 A–H , 2 A–G & 5 .

Type:— BRAZIL. Minas Gerais: Córrego Danta, Distrito de Cachoeirinha , margem leste do trecho de intersecção da rodovia BR-354 com a BR 262 , 19º42’54.8”S 46º01’12.3”W, 1157 m, 2 Sep 2014, M. F. Devecchi & N. Bordon 320 (holotype: SPF!; isotypes: K!, NY!, RB!) .

Similar to Homalolepis praecox but differing by the narrow elliptic to oblong-elliptic or oblong-ovate (vs. ovate to elliptic-ovate) leaflet shape, the acuminate to acute (vs. obtuse with a drip tip) leaflet apex, the narrow and congested inflorescence (vs. wide and loose), the presence of glandular trichomes scattered on the pedicels (vs. glandular trichomes lacking), and the 5.7–6.4 mm (vs. 6.8–7.7 mm) long filaments.

Subshrubs, 0.15–0.3 m tall, geoxylic (with a thickened, ramified underground system, and a very short aerial stem). Leaves imparipinnate, clustered at the aerial stem apex, deciduous; petiole cylindrical, 6.9–8.5 cm long, pubescent only along the upper surface, slightly swollen at base; rachis cylindrical, 20–28 cm long, smooth, pubescent only along the upper surface; petiolules 0.9–1.5 mm long, base not swollen, smooth and glabrescent; leaflets (11–)15–21, opposite or subopposite; blades of the terminal leaflet and of the lateral-distal leaflets 6.8–8.2 × 2.4–2.9 cm, the terminal leaflet widely obovate, the lateral ones narrow elliptic to oblong-elliptic or oblong-ovate, the apex acuminate to acute, the base cuneate or slightly oblique, margin slightly to conspicuously revolute; venation brochidodromous, midvein prominent on the abaxial surface, slightly to sharply sulcate on the adaxial surface, secondary veins slightly sulcate on adaxial surface and slightly prominent on the abaxial surface; leaflet blades chartaceous to subcoriaceous, discolorous, the adaxial surface dark green and shiny, the abaxial surface pale green and dull, laminar glands absent, apical gland generally present but not conspicuously developed, glabrous except for short non-glandular trichomes along the midvein and secondary veins. Inflorescence a congested, subterminal thyrse, the main axis 14–26 cm long, the proximal lateral branches 5–13 cm long, the distal branches gradually shorter towards the apex, puberulent to pubescent, with scattered glandular trichomes; bracts 1.5–4.8 × 1.1–2.3 mm obovate to spathulate, reddish-green, puberulent, tip swollen with a gland or the whole bract modified as an obovoid gland. Floral buds oblong to oblong-obovoid. Flowers: pedicel 3.4–4.6 mm long, pubescent, with scattered glandular trichomes; calyx green to ferrugineous, externally pubescent, internally glabrous, tube and lobes of equal length; sepals (4–)5(–6), apex obtuse; petals (4–)5(–6), slightly imbricate, 9–12 × 3.1–4.2 mm, oblong to oblong-obovate, apex acute to rounded, cream to greenish, turning yellowish, with few and short trichomes internally, pubescent externally; stamens (9–)10(–12); filaments 5.7–6.4 mm long, terete, glabrous, the adaxial appendage 2.5–3.1 mm long, apex obtuse to rounded, slightly reflexed and obscuring the ovary, not forming a pseudotube by intertwining of the trichomes, the basal half of the appendage adnate to the filament, the distal half free, abaxially villous, adaxially glabrous; anthers dorsifixed, ca. 1.4 mm long, yellow; gynophore subterete, slightly 10–costate, 1.1–1.3 mm long, pubescent; ovary ca. 1.6 mm long, velutinous; style subterete, 1.3–4.6 mm long, bristly near the base; stigma slightly (4–)5(–6)–lobed. Fruits not seen.

Additional specimen examined (paratype):— BRAZIL. Minas Gerais: Córrego Danta, Distrito de Cachoeirinha, margem leste da rodovia ligando Campos Altos a Tapiraí (trecho da intersecção da BR 262 com a BR 354), do lado oposto ao povoado Cachoeirinha, 19 ° 42’55.4”S 46 ° 01’16.7”W, 1090 m, 2 October 2015, J. R. Pirani et al. 6591 ( SPF!)

Etymology:— The specific epithet planaltina refers to the Portuguese word “planalto”, referring to the habitat of the new species, on top of flat tableland (“chapada”) in the Central Brazilian Plateau.

Distribution and ecology:— Homalolepis planaltina has a restricted distribution, known only from the population from which the type and paratype specimens were collected, close to the locality of Cachoeirinha, in Córrego Danta municipality, in the state of Minas Gerais ( Fig. 5 ). The habitat of the new species is a low cerrado vegetation on top of a flat plateau (“chapada”) with a ferrugineous rocky soil, locally called “canga”, which is a conglomerate substrate usually consisting of fragments of iron-formation and hard hematite cemented by limonite and hydrated iron oxide ( Rizzini 1997; Simmons 1968). The vegetation type covering this substrate in the type locality is an open cerrado where treelets of Vochysia spp. ( Vochysiaceae ), Erythroxylum spp. ( Erythroxylaceae ) and Miconia spp. ( Melastomataceae ) prevail. The sites with canga soil are recognized as places harboring either high endemism levels ( Vincent & Meguro 2008) and rare species (sensu Giulietti et al. 2009).

Phenology:— Homalolepis planaltina has been collected in flower in September.

Notes:— The habit of subshrubs with large leaves 26.9–36.5 cm long and terminal thyrsoid bearing flowers with petal length between 9–12 mm long, provided with haired staminal appendages forming a short pseudotube places H. planaltina in Homalolepis sect. Grandiflorae (Engler) Devecchi & Pirani ( Devecchi 2017). This is also supported by strong molecular evidence ( Devecchi 2017). The flowers of the new species are similar but smaller than those of Simaba praecox Hassler (1907: 723) (to be transferred to Homalolepis ), in all of its parts: the pedicel is 3.4–4.6 mm long (vs. 4.1–6.4 mm), the filaments are 5.7–6.4 mm long (vs. 6.8–7.7 mm) and the staminal appendages 2.5–3.1 mm long (vs. 3.4–3.7 mm). Flowers of the two species also differ in the extension of the adnate and free parts of the staminal appendages. Moreover, the two species display remarkable allopatric distributions. S. praecox is endemic to open areas with sandy soils surrounded by forests in the northern region of the department of Caaguazú, Paraguay and in Bolivia near the limits with Paraguay at elevations of 315–500 m (Cavalcante 1983; Pirani 1987; Devecchi 2017). Homalolepis planaltina is known only from Minas Gerais state, southeastern Brazil, at elevation of 1090–1157 m. ( Fig. 5 ).

The occurrence of scattered tetramerous and hexamerous flowers in the inflorescences of H. planaltina is not unusual in the genus; similar situation was recently reported in a study of floral structure of four other species (Alves et al. 2017).

Conservation status:—“ Critically endangered” - CR A4cd; B2b (ii,iii,iv,v)+ D1- The occurrence of Homalolepis planaltina is associated with patches of highland vegetation in the cerrado domain. The species has a restricted distribution (AOO = 8 km 2) and is under threat, with a very small population size, and projected reductions in area of occupancy, habitat quality, and subpopulations of mature individuals.

The new species has a population of ca. 50 mature individuals and it occurs outside of any protected area (the nearest ones are the State Park of Campos Altos, ca. 8 km W of the type locality; and the Serra da Canastra National Park, further west). The main threats are the expansion of agricultural crops and degradation of native vegetation and soils. The area of occurrence of the species lies very close to the small village of Cachoeirinha. In addition, the species is threatened by the local use of its underground stem for medicinal purposes. It is estimated a high population reduction to 80% considering the loss of habitat and the threats incidents in the last 80 years and level of exploitation of medicinal plant projected for the next 20 years. Efforts have been made recently by experts to search for other subpopulations in the region and areas with similar vegetation, but without success so far.

Figures

FIGURE 1. Homalolepis planaltina. A. Habit, vegetative stage. B. Stem thickened with underground development. C. Portion of a leaf showing the opposite and subopposite leaflets. D. Habit, reproductive stage; the inflorescence grows near ground level. E. Flower F. and G. Stamens with anther, filament and filament appendage. H. Flower with petals removed showing the gynoecium on top of a gynophore and style (A–H. Devecchi & Bordon 320).

FIGURE 2. Homalolepis planaltina. A. Habit. B. Apex of a leaflet showing the gland. C. Distal part of the inflorescence with floral buds and glandular bracts. D. Underground system with a young inflorescence. E. Individual with ramified underground system, the inflorescence and leaves located on different branches. F. Flowers with five and six petals on a same inflorescence. G. Individual in reproductive stage, without leaves.

FIGURE 5. Map showing the distribution of the two new species and their closely related species.