Drosera spirocalyx Rivadavia & Gonella, 2014

Rivadavia, Fernando, Gonella, Paulo Minatel, Sano, Paulo Takeo & Fleischmann, Andreas, 2014, Elucidating the controversial Drosera montana complex (Droseraceae): a taxonomic revision, Phytotaxa 172 (3), pp. 141-175 : 155-158

Drosera spirocalyx Rivadavia & Gonella , sp. nov. ( Figs. 5 , 6 , 7 )

Type: — BRAZIL. Minas Gerais: Santana do Riacho , trilha para velózias gigantes, 12 September 1999, Rivadavia 1165 (holotype SPF!; isotypes BHCB!, P!) .

Diagnosis: —Species similar to Drosera tentaculata Rivadavia , but differs in the oblanceolate to narrowly obovate leaves densely covered by white eglandular trichomes on the adaxial petiole surface and whole abaxial leaf surface, apical tentacles much less developed, shorter scapes, and sepals sub-orbicular to broadly ovate in shape with rounded apex, overlapping (torsive or spirally contorted aestivation) when in bud and the lateral margins of adjacent sepals forming a pyramidal projection where fused at their bases.

Description: —Perennial rosetted herbs, often forming short upright or prostrate stems up to 3 cm in length, densely covered by persistent dead leaves. Roots slightly succulent, sparsely branched, black, densely covered with root hairs. Indumentum consists of a dense cover of white eglandular trichomes (pale brown when dried) on the abaxial leaf surface, adaxial petiole surface and base of the scape; capitate glandular trichomes on scape, bracts, pedicels and sepals; sparse minute sessile glands ca. 0.03 mm in diameter on leaves and inflorescence parts. Leaves 3.5–15 mm long, with circinate vernation, decumbent, oblanceolate to narrowly obovate, apex obtuse to sub-truncate, green to wine red in color, usually bicolored with the petiole greener than the lamina; petiole 1.3–6.1 mm long, 0.4–1.6 mm wide, densely eglandular-pilose (villous) on both surfaces; lamina 2.2–8.9 mm long, 1.5–3.6 mm wide, abaxial surface densely eglandular-pilose, decreasing in density towards apex, adaxial surface covered with numerous red, motile, capitate tentacles with radial symmetry, the apical tentacles inconspicuously distinct, 6–8 in number, 3–4 mm long, stalk up to 0.2 mm wide at base, the head oblong, up to 0.3 mm long with unifacial gland tip; stipules 2–4 mm long, 0.3–1.1 mm wide at the base, rectangular, membranaceous, translucent white to reddish (drying bronze colored), the apical 2/3–1/2 divided into 3 segments, the lateral ones longer, narrower, and poorly divided or entire, the central one shorter, broader, and with fimbriate apex. Scapes 1–3, erect from the base, 14–82(–105) mm long (including floriferous part), terete, green to deep red in color, covered with glandular trichomes uniform in size, sparse on the basal half, increasing in density towards apex, often sparsely eglandular-pilose in the basal third; inflorescence a scorpioid cyme bearing 1–4 flowers, rarely bifurcating; bracts caducous, usually absent on mature scapes, 0.2–1.5 mm long, linear, glandular-pilose abaxially; pedicels 0.6–3 mm long, inserted 3.3–7.5(–9.5) mm apart, densely glandular-pilose; sepals 5, 2– 4.2 mm long, 1.7–2.8 mm wide, sub-orbicular to broadly ovate, united at basal 2/5 of length, overlapping (torsive or spirally contorted) when in bud with the lateral margins forming a pyramidal projection at the fusion point between adjacent sepals, apex rounded (rarely subobtuse), sparse to densely glandular-pilose abaxially; petals 5, (3.5–) 5–7.5 mm long, 4.8–6.1 mm wide, obovate, light to dark pink in color; stamens 5, 2– 3.8 mm long, filaments white to light pink, anthers 0.5–1 mm long, bithecate, yellow; ovary 3-carpellate, fused, 1–2 mm in diameter, ovoid, subglobose to trilobed in outline; styles 3, forked at the base, 1.4–3 mm long (including stigmata), pale pink in color, style arms curving inwards at the end of anthesis, stigmata 2–3 lobed or cordiform; fruit a dry dehiscent capsule, 2–3 mm long, ellipsoid, 3-valvate; seeds ca. 0.7 mm long, ca. 0.25 mm wide, ellipsoid to oblong, black, testa reticulate.

Distribution and ecology: — Drosera spirocalyx is a narrow endemic species, known only from the centralsouthern region of the Serra do Cipó, in Minas Gerais state ( Fig. 5 ). It has been observed growing in campo rupestre vegetation near or sympatric with D. chrysolepis , D. quartzicola , D. hirtella var. hirtella , D. montana , D. tentaculata and D. tomentosa , occupying narrowly defined habitats at elevations between 1000–1350 m. Only around 15 populations of D. spirocalyx are currently known, most of which had ca. 50–100 individuals, although a few large populations contained hundreds of plants.

The majority of D. spirocalyx populations were found in sandy quartzitic soils or borderline habitats where sandy soils meet mounds of white quartz gravel mixed with fine sand (a habitat also typical of D. quartzicola , D. schwackei , and D. tentaculata ). A few populations were observed in disturbed areas along trail sides, growing in fine white sandy soil, or on the margins of natural water drainages.

Compared to other Drosera species , D. spirocalyx occupies relatively dry habitats far from springs and other more reliable water sources. Although their habitats may receive plenty of rain in the summer wet season, the main source of water in the dry season appears to be condensation at night. As a result, the rosettes of D. spirocalyx become less vigorous in the dry season, producing shorter leaves that often lack mucilage on the carnivorous tentacles. However, this species surprisingly never retreats into complete dormancy underground, as does D. montana .

The flat rosettes of D. spirocalyx (as well as those of D. montana and D. tentaculata ) are often observed somewhat covered with sand adhering to the stipules and hairs on the petioles, which may possibly act to protect the plants from excessive heat exposure and evaporative loss.

An interesting feature observed in some D. spirocalyx populations is the presence of globose clumps of plants containing dozens of rosettes ( Fig. 7A ), suggesting a possible clonal origin by lateral budding from the roots.

Phenology: — Drosera spirocalyx produces flowers during the height of the dry season, extending into the early wet season, between July to November, which corresponds to late winter and early spring.

Etymology: —The specific epithet “ spirocalyx ” was chosen due to the characteristic broad sepals of this new species, which spirally overlap each other in the flower bud and often after anthesis ( Figs. 6G–H ; 7C, E ).

IUCN Red List Category: —Although locally somewhat common in the central-southern region of the Serra do Cipó, D. spirocalyx presents a very restricted area of occurrence. Most of the known populations lie outside the protected area of the national park and are vulnerable to habitat destruction by cattle farming and mining activities, possibly facing a threat in the near future. Thus, D. spirocalyx is here considered as Vulnerable (VU) according to the IUCN criteria B2a, biii ( IUCN 2001).

Discussion: — Drosera spirocalyx can be easily recognized by the often bicolored leaves with green petioles and wine red lamina (a characteristic shared with D. tentaculata ), the villous adaxial petiole surface and whole abaxial leaf surface, the short scapes with few flowers (up to 4), and by the sub-orbicular to broadly ovate sepals with rounded (rarely subobtuse) apex. The sepals of this species are unique among New World Drosera as their margins partially overlap in bud (contorted aestivation), forming a pyramidal projection at the fusion point between adjacent sepals, a character only found in one other, unrelated, species of Drosera , D. stenopetala Hooker (1853: 19) from New Zealand (A.F. pers. obs.).

The relatively broad sepals of D. spirocalyx are more rigid than those of other species in the D. montana complex, and are likely to aid in seed dispersal. When the fruit matures, the capsule and calyx open in a way similar to (but not as pronounced as) the splash-cups found in D. felix , D. kaieteurensis , and D. solaris Fleischmann, Wistuba & McPherson (2007: 1) ( Rivadavia 1999; Fleischmann et al. 2007).

Drosera spirocalyx is apparently most closely related to D. tentaculata , sharing characteristics such as bicolored leaves with apex often sub-truncate, occasionally forming columns of dead leaves, as well as similar habitats and flowering season (for distinguishing characters, see Table 1).

Specimens of D. spirocalyx were considered as either D. montana var. montana or D. montana var. tomentosa by Silva (1994).

Additional specimens examined (paratypes) — BRAZIL. Minas Gerais: Município de Conceição do Mato Dentro, Parque Natural Municipal do Ribeirão do Campo, 13 September 2002, Mota & Viana 1913 (BHCB). Município de Santana do Riacho, Fazenda Palácio, 22 December 1948, Palacios et al. 3601 (R); km 129 da rodovia Belo Horizonte- Conceição do Mato Dentro, 6 October 1981, Cordeiro et al. CFSC 7533 (SP, SPF); trilha para as Velózias gigantes, 09 July 1999, Rivadavia et al. 1095 (SPF), 07 September 2002, Rivadavia 1410 (SPF), 12 November 2007, Gonella et al. 44 (SPF), 15 May 2008, Gonella et al. 73 (SPF), 15 May 2008, Gonella et al. 80 (SPF); acampamento Serra Morena, 28 July 2002, Rivadavia & Gibson 1361 (SPF); 2.5 km após acampamento Serra Morena, 28 July 2002, Rivadavia & Gibson 1363 (SPF); após acampamento Serra Morena, 07 September 2002, Rivadavia 1411 (SPF), 04 April 2003, Rivadavia 1541 (SPF), 29 January 2005, Rivadavia 1937 (SPF), 23 May 2009, Gonella et al. 234 (SPF), Gonella et al. 235 (SPF), Gonella et al. 236 (SPF), Gonella et al. 245 (SPF), Gonella et al. 246 (SPF); km 112 da MG-10, trilha para o canyon do Travessão, 04 April 2003, Rivadavia 1545 (SPF), 29 January 2005, Rivadavia 1939 (SPF); 16 May 2008, Gonella et al. 91 (SPF), 20 July 2008, Gonella et al. 134 (SPF), 20 July 2008, Gonella et al. 152 (SPF), 22 July 2008, Gonella et al. 162 (SPF), 06 April 2009, Gonella et al. 219 (SPF), Gonella et al. 223 (SPF), 19 April 2010, Gonella et al. 260 (SPF), 02 September 2011, Gonella et al. 422 (SPF); entre sede do IBAMA e Vellozias gigantes, 21 July 2008, Gonella et al. 139 (SPF), Gonella et al. 140 (SPF).

Figures

FIGURE 5. Distribution map of D. spirocalyx (squares) and D. tentaculata (circles) in eastern Brazil.

FIGURE 6. Drosera spirocalyx. A, habit.B, C, detail of the indumentum at the base (B) and apex (C) of the scape. D, leaf, abaxial surface. E, leaf, adaxial surface. F, stipule. G, calyx showing actual shape of sepals. H, calyx showing the spirally contorted overlap of the sepals. J, petal. K, gynoecium and one stamen seen from above. L, seed. Based on the holotype. Drawn by P.M. Gonella.

FIGURE 7. Drosera spirocalyx. A, habitat, forming a circular clump of rosettes, at the locus classicus. B, a flowering specimen. C, an open flower seen from below, highlighting the sepals. D, detail of a sterile rosette. E, side view of a flower bud, showing the contorted, overlapping sepals with obtuse apex, forming a pyramidal projection where adjacent sepals fuse.All by P.M. Gonella.