Homalolepis pumila 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 : 257-261

Homalolepis pumila Devecchi & Pirani , sp. nov. Figures 3 A–F , 4 A–G & 5 .

Type:— BRAZIL. Goiás: Chapadão do Céu , Parque Nacional das Emas, 18º15’56.3”S 52º53’24.3”W, 788 m, 8 September 2014, M. F. Devecchi & G. Alves 323 (holotype: SPF!; isotypes: NY!, RB!) .

Closely related to Simaba suffruticosa , because of their small habit (reduced subshrubs with a well-developed underground system) and general appearance, but differing from the latter by having only 5–7 leaflets (vs. 9–11(–13)), the presence (vs. absence) of laminar glands scattered near the base of the abaxial leaflet surface, the petals 5.5–6.1 × 1.4–1.8 mm (vs. 7.9–9.1 × 1.9–2.8 mm), and the staminal appendage being adnate to the filament along its whole extension, except for two tooth-like projections (vs. appendage with a free distal portion bearing an obtuse apex).

Subshrubs, 0.1–0.15 m tall, geoxylic (with a ramified, thickened underground system and a very short aerial stem). Leaves imparipinnate, clustered at the stem apex; petiole semi-terete, 1.4–2.1 cm long, pubescent along the entire surface, swollen at base; rachis semi-terete, 2.8–5.2 cm long, smooth, pubescent along the entire surface; petiolules sessile or less than 1 mm long, swollen, slightly wrinkled and pubescent; leaflets 5–7, opposite or subopposite; blades of the terminal and lateral-distal leaflets 5.7–7.6 × 2.4–2.9 cm, the terminal leaflet oblanceolate to obovate, the lateral ones obovate to oblong-obovate or oblanceolate, the apex acute to obtuse, the base attenuate in the terminal leaflet and cuneate in the lateral ones, margin not revolute; leaflet venation brochidodromous, midvein prominent on the abaxial surface, slightly to sharply sulcate on the adaxial surface, secondary veins slightly prominent on the abaxial surface and slightly sulcate to immersed on adaxial surface; laminar glands present on the basal third portion of the lamina, scattered among the secondary veins arches on abaxial surface; leaflet blade with an apical gland generally present at the apex, not conspicuously developed, chartaceous, discolorous, the adaxial surface dark green and shiny, the abaxial surface pale green and dull, sparsely pubescent on both surface, the trichomes mainly restricted to the midvein, glandular trichomes if present scattered along the midvein region on adaxial surface. Inflorescence a congested, terminal or lateral thyrsoid, the main axis 3–6 cm long, the proximal secondary branches 1.4–3.1 cm long, the distal branches gradually shorter towards the apex, pubescent, glandular trichomes absent; bracts 1.9–2.5 × 0.5–0.7 mm, spathulate to linear, green, puberulent, tip slight swollen, generally with a gland on the tip. Floral buds obovoid to oblong-obovoid. Flowers: pedicel 3.9–4.8 mm long, pubescent, glandular trichomes absent; calyx green, externally pubescent, internally glabrous, length ratio between tube and lobes 1:5; sepals 5, apex acuminate; petals 5, slightly imbricate, 5.5–6.1 × 1.4–1.8 mm, oblong, apex acute, cream to greenish turning yellowish, pubescent to puberulent on both surfaces, apex acute; stamens10; filaments 3.6–3.9 mm long, terete, glabrous, provided with an adaxial appendage 2.6–2.9 mm long, adnate to the filament along its whole extension except for two distal tooth-like projections, abaxially glabrous, adaxially sericeous, the appendages united by the intertwining of the trichomes but not forming a pseudotube, slightly reflexed, obscuring the ovary; anthers dorsifixed, 0.7–0.9 mm long, white to cream; gynophore subterete to conical, slightly 10–costate, ca. 1.1 mm long, pubescent to sericeous; ovary 0.9–1.2 mm long, sericeous; style subterete tapering towards the apex, 1.2–1.8 mm long, bristly near the base; stigma slightly lobed. Fruits composed of 1–4 drupaceous mericarps (drupelets), when immature 0.9–1.3 × 0.7–1.3 cm, broadly ellipsoid, green, pubescent, with a single seed.

Additional specimens examined (paratypes):— BRAZIL. Goiás: Chapadão do Céu , Parque Nacional das Emas, 17º49’S 52º39’W, fl., 5 August 1999, M. A. Batalha 3730 ( SP!) ; ibidem, 18º28’S 53º19’W, fr., 6 October 1999, M. A. Batalha 3939 ( SP!) ; Mineiros, Parque Nacional das Emas, fl., fr., 7 September 1999, M. A. Batalha 3810 ( SPF!) ; ibidem, fl., fr., 10 September 1999, M. A. Batalha 3883 ( SPF!) ; ibidem, estrada distante ca. 2.3 km a esquerda do Portão Jacuba, fl., 27 July 2017, M. F. Devecchi et al. 467 ( SPF!) .

Etymology:— The epithet pumila derives from the Latin word pumilus, meaning dwarf, and refers to the reduced habit of this species.

Distribution and ecology:— The only three populations known of Homalolepis pumila lie within the limits of the Emas National Park, between the municipalities of Chapadão do Céu and Mineiros, in the southwestern region of the Goiás State, Central Brazil ( Fig. 5 ). It is one of the largest reserves of the Cerrado vegetation type ( Fonseca et al. 2000), being nested within the Cerrado core region at Brazilian Central Plateau. The prevailing soils in the Emas National Park are basaltic but several rock outcrops occur with high content of Fe 2 O 3 ( RADAMBRASIL 1983). The new species is restricted to the physiognomy of campo sujo, which is an open, mostly herbaceous to shrubby savanna of wide occurrence throughout the Brazilian cerrado. Homalolepis pumila is a small subshrub with geoxylic habit. This dwarf life-form is likely to enable the cerrado species to cope with drought and fire disturbance (e.g. Rizzini & Heringer 1961; Simon et al. 2009). As is the case in some other dwarf species of Homalolepis , along with several other subshrubs in the Cerrado, the new species shed all or most of its leaves during the dry season, and the flowering starts before the new leaves are borne ( Fig. 4 E, F ). The development of axillary inflorescences, a very uncommon character in Homalolepis , was observed in several individuals of the new species. Additionally, the formation of the peduncle and axillary flowering branches may take place partially below ground level. While growing, these axillary inflorescences are very condensed and devoid of green pigment ( Fig. 4 D ). The flowers open very near to ground level ( Fig. 3A, B ; 4 A, B ). Studies on the floral biology of this species would be interesting.

Phenology:— Homalolepis pumila has been collected with flowers and immature fruits in August and September, and with mature fruits in October.

Notes:— The habit of subshrubs with small leaves (4.2–7.3 cm long), and floral features of its stamens and gynophore place H. pumila in H. sect. Homalolepis . An update of characters distinguishing this section (as Simaba sect. Floribundae ) from H. sect. Grandiflorae was provided by Devecchi & Pirani (2015) and Devecchi et al. (2016). Homalolepis pumila is morphologically close to S. suffruticosa Engler (1874: 213) (to be transferred to Homalolepis ), but differs from the latter by bearing fewer leaflets 5–7 (vs. 9–11[–13]), with laminar glands scattered near the base of the abaxial leaflet surface (vs. glands lacking), by the petals 5.5–6.1 × 1.4–1.8 mm (vs. 7.9–9.1 × 1.9–2.8 mm), and by the appendage being adnate to the filament along its whole extension, except for the distal lateral projections ending in two lateral projections (vs. appendage with a free distal portion bearing an obtuse apex). A phylogenetic analysis also provides significant differences in both nuclear ITS, ETS and plastidial trn LF sequences of these two species ( Devecchi 2017). Moreover, they are conspicuously allopatric ( Fig. 5 ).

Conservation status:— “Vulnerable” (VU–D2). A GeoCAT analysis and IUCN (2014) criteria suggest that Homalolepis pumila should be classified as Vulnerable. (EOO = 483.678 km 2; AOO = 16 km 2). This new species is known only from some populations inside the Emas National Park. Because of its restricted area of occupancy, any change in the environment of any of the known populations could require that the species should be transferred to a higher risk category in the near future.

Figures

FIGURE 3. Homalolepis pumila. A. Habit, the inflorescence at ground level. B. Individual bearing only flowers, before leaf sprouting. C. Flower. D. Stamen bearing a laminar appendage. E. Distal portion of the style showing the stigma lobed. F. Two fruits, one with four drupelets, the other with only one (A–H. Devecchi & Alves 323).

FIGURE 4. Homalolepis pumilaA. Habit. B. Flowers at anthesis. C. Habit, showing the underground system and inflorescence at ground level. D. Underground system with sprouting lateral inflorescences. E. An individual bearing only flowers, lateral view. F. View from above of the plant shown in E. G. Habitat of the new species: open cerrado physiognomy.

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