Drosera quartzicola Rivadavia & Gonella, 2011

Rivadavia, Fernando & Gonella, Paulo Minatel, 2011, Drosera quartzicola (Droseraceae), a new and threatened species from the Serra do Cipó, Brazil, Phytotaxa 29, pp. 33-40 : 34-39

Drosera quartzicola Rivadavia & Gonella , sp. nov. ( Figs. 1 , 2 , 3 & 4 )

Drosera chrysolepis affinis , sed caulis brevis ad 4 cm longis, petiolis laminis aequantibus vel paulo brevioribus, in laminas continuos, pilis eglandulosis tantum in pagina foliorum inferiore, et scapis brevioribus differt.

Holotype:— BRAZIL: Minas Gerais: Santana do Riacho, km112-113 da estrada para Conceição do Mato Dentro (MG-10), em morro após bifurcação da trilha para o Travessão e cachoeira Congonhas , seguindo à esquerda, 1360 m, 19 April 2010, P. M. Gonella et al. 264 ( SPF).

Perennial rosetted herbs, acaulescent, sometimes forming short stems covered by the persistent dead leaves, up to 4 cm high; white eglandular hairs 0.5–3.0 mm long, present on leaves (abaxially, denser and longer towards the base), scapes, pedicels, and sepals (abaxially); minute sessile glands c. 0.03 mm diam., sparsely present on leaves (abaxially and adaxially), scapes, pedicels, and sepals (abaxially); translucentyellow short-stalked multicellular globose trichomes (from here on referred to as ‘TSG’ trichomes) 0.10–0.15 mm in diameter present on lamina (abaxially), petioles (adaxially and abaxially), pedicels, and sepals (abaxially). Stipules triangular, membranaceous, 6–8 mm long, 1.5–3.0 mm wide at the base, bronze-gold in color, the apical ½–⅓ divided into 2–3 long laciniate segments with fimbriate apex. Leaves with circinate vernation, semi-erect, patent when old, lanceolate, (7–) 10–40 mm long; petioles (3.5–) 5–20 mm long, 0.8–2.4 mm wide, yellowish-green to red in color; lamina (3.5–) 5–20 mm long, 1.2–2.5 mm wide, yellowish-green to red in color, adaxial surface covered with numerous red, carnivorous, capitate tentacles. Scapes 1–2(–3) per plant, erect or slightly curved at the base, apex often bifurcate, 1.7–11.5 cm long; inflorescence a scorpioid cyme, bearing 1–9(–11) flowers; bracts filiform-lanceolate, 1.5–3.6 mm long, usually absent; pedicels 1.5–6 mm long, inserted 3.6–15.0 mm apart from each other; sepals 5, oblong-lanceolate to lanceolate, 2.5–7.5 mm long, 0.7–2.0 mm wide, united at basal ⅓–¼ of length; petals 5, obovate, 5.5–10.1 mm long, 4.5–7.0 mm wide, pink-lilac in color; stamens 5, 3– 4 mm long, anthers 1.0– 1.7 mm long, bithecate, yellow; ovary 3- carpellate, ellipsoid, 1.5–2.0 mm in diameter at anthesis, slightly 3-lobed in outline; styles 3, forked at the base, 3–4 mm long (including stigmata), stigmata flabellate, pink-lilac to dark pink in color; fruit a dry capsule, ellipsoid, 2.5–3.0 mm long, 3-valvate; seeds narrowly oblong-ovate, 0.7–0.8 mm long and c. 0.3 mm wide, testa reticulate, black.

Distribution and ecology: — Drosera quartzicola is endemic to the Serra do Cipó in central Minas Gerais state, southeastern Brazil. It was observed growing sympatrically with D. tentaculata and D. chrysolepis in ‘campo rupestre’ vegetation, where it seems to have the same ecological niche occupied further north along the Cadeia do Espinhaço by D. schwackei . Both D. quartzicola and D. schwackei grow in small populations in fine silica sand mixed with white quartz gravel among sparse grasses and sedges ( Fig. 2C ), often concentrated along a borderline habitat, where mounds or hillsides with this soil meet flatter sandier areas. This habitat is usually humid from constant rainfalls during the summer wet season, but in winter it becomes very dry when compared to other seasonal habitats occupied by Drosera species in Brazil.

The rosettes of D. quartzicola (similar to those of D. schwackei ) lose vigor during the winter dry season. With decreasing soil moisture, the leaves become reduced in length, curl inwards, and the sticky carnivorous tentacles may even lose their mucilage ( Fig. 2B ). The main source of water during the winter is probably from dew, which condenses on the tentacles, eglandular hairs, and TSG trichomes.

The semi-erect leaves of D. quartzicola were observed in the field to capture mostly flying insects, such as small flies and mosquitoes (Diptera).

Phenology: —As a result of its preference for drier habitats, D. quartzicola flowers very early in the wet season, from January to February, although a few individuals have been collected with flowers in April.

Etymology: —The epithet “ quartzicola ” denotes the characteristic habitat of this new species, occurring in silica sand mixed with white quartz gravel.

Drosera quartzicola belongs to Drosera subgen. Drosera sect. Drosera (sensu Seine & Barthlott 1994) and superficially resembles D. schwackei , with which it shares similar leaf shape and size, heavy eglandular pubescence on the abaxial leaf surface, abundance of TSG trichomes, and relatively large oblong-ovate seeds with similar ornamentation. All this suggests a possible close relationship between D. quartzicola and D. schwackei , or else a convergence of ecological adaptations to strikingly similar habitats. Drosera schwackei can be readily distinguished by its shorter rectangular stipules (1–4 mm long), and further by its oblonglanceolate leaves, which are usually shorter (up to 22 mm) and wider (up to 4 mm), longer scapes (6–18 cm in length), its more compact and yellowish rosettes, shorter petioles (up to 5 mm), eglandular hairs present on the adaxial surface of petioles, and smaller TSG trichomes c. 0.05 mm in diameter (0.10–0.15 mm in D. quartzicola ).

Notwithstanding the above similarities with D. schwackei , D. quartzicola is probably most closely related to (and in many ways resembles a morphologically reduced specimen of) D. camporupestris , D. graminifolia Saint-Hilaire (1824: 269) , and especially D. chrysolepis . Similar to D. schwackei , these taxa share characters such as TSG trichomes ( Figs. 3D , 4A & B ) and relatively large oblong to ovate seeds with similar ornamentation, but D. schwackei does not possess the unusually large bronze-colored triangular stipules found in the other four species. Drosera quartzicola is morphologically most similar and possibly most closely related to D. chrysolepis , with which it has even been observed to form natural hybrids at one population. Drosera quartzicola can be easily distinguished from D. camporupestris , D. chrysolepis , D. graminifolia , and D. schwackei when in flower by its much shorter inflorescences, possibly an adaptation to the more exposed and drier montane habitats where it occurs.

The TSG trichomes observed in D. quartzicola , D. schwackei , D. camporupestris , D. chrysolepis , and D. graminifolia , are also present in D. meristocaulis Maguire & Wurdack (1957: 332) ( Drosera sect. Meristocaules ) native to Venezuela, and in some members of the so-called ‘pygmy Drosera ’ ( Drosera sect. Bryastrum ), of Australia and New Zealand. It appears that the TSG trichomes are not secretory in nature, but are hygroscopic organs used by the above species (which inhabit relatively very dry habitats for Drosera ) to absorb humidity from the air. When air humidity is low, the TSG trichomes appear to be slightly moriform, but in more humid conditions become globose and smooth when intumesced, and even appear to collect water at the apex, resembling a glandular trichome (A. Fleischmann, personal communication). The TSG trichomes resemble smaller versions of the moriform trichomes found on the petioles of D. hartmeyerorum Schlauer (2001: 104) from northern Australia, and may be homologous with these.

Drosera quartzicola is the rarest of the known sundews native to Brazil. Although extensive searches have been carried out, it is still only known from four small populations in the Serra do Cipó highlands. Three of these populations are found at an elevation of about 1350 m and contain approximately 60, 100 and 120 plants, whilst the fourth is located at an elevation of 1100 m and contains approximately 20 individuals.

The D. quartzicola populations with c. 60 and 100 individuals are barely within the borders of the Serra do Cipó National Park, and the latter of these two is unfortunately located on the margins of a touristic trail, which is a source of erosion and invasion of exotic grasses (such as Melinis and Brachiaria species ) usually associated with cattle, that frequently cross into the park in this area. The largest population (with c. 120 plants) is found just outside the park, also in an area with the occasional presence of cattle. The smallest D. quartzicola population (with c. 20 plants) is located outside the park, approximately six kilometers north of the other three populations.

Based on the IUCN criteria ( IUCN 2001), we hereby propose to list D. quartzicola as “Critically Endangered”, due to its restricted occurrence in an area estimated to be less than 100 km 2, the projected decline in the quality of the habitat, and the small total population size.

Addicional specimens examined (paratypes): — BRAZIL. Minas Gerais: Santana do Riacho, km 115 da estrada para Conceição do Mato Dentro , 12 March 1993, Silva CFCR 13035 ( SPF) ; Santana do Riacho, km 112-113 da estrada para Conceição do Mato Dentro , em morro após bifurcação da trilha para o Travessão e cachoeira Congonhas, seguindo à esquerda , 22 February 1996, Rivadavia & Mullins 542 ( SPF) , 22 July 2008, Gonella et al. 151 ( SPF) , 6 April 2009, Gonella et al. 222 ( SPF) ; Santana do Riacho, km 112-113 da estrada para Conceição do Mato Dentro , em morro à esquerda logo no início da trilha para o Travessão e cachoeira Congonhas , 25 February 1997, Rivadavia & Pinheiro 555 ( SPF) , 12 September 1999, Rivadavia 1163 ( SPF) , 28 July 2002, Rivadavia & Gibson 1359 ( SPF) , 29 January 2005, Rivadavia 1938 ( SPF) , 20 July 2008, Gonella et al. 132 ( SPF) , 6 April 2009, Gonella et al. 218 ( SPF) ; Santana do Riacho , após acampamento Serra Morena , 7 September 2002, Rivadavia 1412 ( SPF) , 29 January 2005, Rivadavia 1936 ( SPF) ; Santana do Riacho, km 112-113 da estrada para Conceição do Mato Dentro , em morro à direita logo no início da trilha para o Travessão e cachoeira Congonhas , 4 April 2003, Rivadavia 1544 ( SPF) , 20 July 2008, Gonella et al. 133 ( SPF) , 6 April 2009, Gonella et al. 224 ( SPF) .

Figures

FIGURE 1: Drosera quartzicola Rivadavia & Gonella. A. Habit. B. Calyx. C. Stipule. D. Seed. E. Leaf, adaxial surface. F. Leaf, abaxial surface. Based on the holotype.

FIGURE 3. Drosera quartzicola. A. Front view of the flower. B. Close-up of the front view of the flower, detail of the reproductive organs. C. Close-up of the flower bud, showing the dense indumentum of eglandular hairs and translucentyellow short-stalked globose (‘TSG’) trichomes. D. Close-up of the adaxial surface of the petiole, showing the large number of TSG trichomes. Photos by P. M. Gonella.

FIGURE 4. SEM micrographs of the translucent-yellow short-stalked globose (‘TSG’) trichomes and the minute sessile glands of Drosera quartzicola. A. Adaxial surface of the petiole with multiple TSG trichomes (the ones on the left showing a somewhat moriform shape) and minute sessile glands; B. Lateral view of a single TSG trichome and smaller sessile gland. Micrographs provided by A. Fleischmann.

FIGURE. 2. Drosera quartzicola. A. View of a rosette towards the end of the wet season (April). B. View of a rosette at the start of the dry season, with leaves curved inwards (July). C. View of the habitat, silica sand mixed with white quartz gravel. A by F. Rivadavia; B & C by P. M. Gonella.