Drosera tomentosa Saint-Hilaire (1826: 261)

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 : 163-166

Drosera tomentosa Saint-Hilaire (1826: 261) ( Figs. 10–14)

Type (lectotype here designated):— BRAZIL. Minas Gerais: Crescit in paludosis montium propè Itambé, without date, Saint-Hilaire M- 378 (P-749166!, fifth specimen from the left ( Fig. 14 ); isolectotypes P!, K(the two plants on the top right) image!, MPU image!) .

≡ Drosera montana A.St. -Hil. var. tomentosa ( Saint-Hilaire 1826: 261) Diels (1906: 89) .

Description: —Perennial rosetted herbs, often forming short upright or prostrate stems up to 2 cm in length, densely covered by persistent dead leaves. Roots slightly succulent, sparsely branched, black, densely covered with root hairs. Indumentum consists of white eglandular trichomes (pale brown when dried), on the abaxial leaf surface, often on the adaxial petiole surface and from base to apex of scape, rarely on pedicels and sepals; capitate glandular trichomes on scape, bracts, pedicels and sepals; and minute sessile glands ca. 0.03 mm in diameter on leaves and inflorescence parts. Leaves (2.5–) 4–24 mm long, with circinate vernation, decumbent (the youngest leaves sometimes semi-erect), obovate to oblong-obovate, rarely oblong, apex obtuse, green to wine red in color; petiole (0.5–) 1–8 mm long, 0.4–3 mm wide, abaxial surface sparse to densely eglandular-pilose, adaxial surface glabrous to sparsely eglandular-pilose (very rarely densely eglandular-pilose); lamina (2–) 3–17 mm long, 1.3–6 mm wide, abaxial surface sparsely eglandular-pilose, trichomes concentrated towards the base and along the margins, adaxial surface covered with numerous red, motile, capitate tentacles with radial symmetry, the apical tentacles usually inconspicuously distinct, 5–9 in number, up to 5 mm long, stalk up to 0.3 mm wide at base, the head ellipsoid to rectangular-linear, up to 0.6 mm long with unifacial gland tip; stipules 1.5–4 mm long, 0.5–2 mm wide at the base, rectangular, membranaceous, translucent white in color (drying bronze colored), the apical 1/2–1/3 divided into several laciniate segments, the middle segments shorter than the lateral ones. Scapes 1–3, erect from the base, (10–) 28–330 mm long (including floriferous part), terete, green to deep red in color, erect at the base, glandular trichomes absent on the basal third (only sessile glands present), but increasingly denser and longer towards the apex, eglandular trichomes absent to dense from base to apex, usually decreasing in density towards the apex; inflorescence a scorpioid cyme bearing 1–23 flowers, rarely bifurcating; bracts caducous, usually absent on mature scapes, (0.4–) 0.7–2 mm long, lanceolate to narrowly ellipsoid, densely glandularpilose and rarely sparsely eglandular-pilose abaxially; pedicels 0.7–6 mm long, inserted 2–20 mm apart, densely glandular-pilose rarely bearing sparse eglandular trichomes; sepals 5, 1.5–3 mm long, 0.6–1.3 mm wide, narrowly ovate to oblong-ovate, united at basal 1/3–1/5 of length, apex acute, densely glandular-pilose abaxially, rarely with sparse eglandular trichomes; petals 5, 2– 5 mm long, 2.5–4 mm wide, narrowly to broadly obovate or cuneate, light to dark pink in color; stamens 5, 1.5–4 mm long, filaments white to light pink, anthers 0.4–0.8mm long, bithecate, yellow; ovary 3-carpellate, fused, 0.5–1.3 mm in diameter, ellipsoid to globose, trilobed or hexalobed in outline; styles 3, forked at the base, 1.2–3 mm long (including stigmata), pale pink in color, style arms curving inwards at the end of anthesis, stigmata flabellate, cupullate, bilobed, or more rarely bifurcate; fruit a dry dehiscent capsule, 1.1–2.3mm long, ellipsoid, 3-valvate; seeds 0.45–0.7 mm long, 1.5– 0.25 mm wide, ovoid to ellipsoid, dark brown to black, testa reticulate.

Illustrations: — Ferrero & Mello-Silva (2011: 15, fig. 1D–F— D. tomentosa var. glabrata ).

Distribution and ecology: — Drosera tomentosa is endemic to Brazil, occurring in the states of Sergipe, Bahia, Goiás, and Minas Gerais ( Fig. 10), where it mostly grows in montane to high-montane habitats at elevations between 700-2050 m. It is widespread and abundant in campo rupestre vegetation in central-eastern Brazil and is especially common along the Espinhaço Range, from southern Minas Gerais to the Chapada Diamantina, in Bahia. In Minas Gerais it furthermore spreads east to the Pico da Aliança, southwest to the Serra da Canastra and southeast to the Serra da Mantiqueira (Aiuruoca and Serra de Ibitipoca), possibly extending just over the border in São Paulo and Rio de Janeiro states. In Goiás, D. tomentosa occurs disjunctly at the Chapada dos Veadeiros, in the northeastern part of the state.

An isolated collection of D. tomentosa is also known from the Serra de Itabaiana highlands in the state of Sergipe, northeastern Brazil. This is a sandstone escarpment reaching nearly 700 m altitude, located in a relatively hot region of Brazil, and it represents the northeastern distribution limit of D. tomentosa .

Drosera tomentosa , D. chrysolepis , and D. communis share a very interesting pattern of disjunct distribution (geographically and ecologically). Although most populations in Brazil occur on relatively temperate highlands, above 700 m elevation, these three taxa also extend into hot coastal restinga habitats just above sea level, at several locations along the northern coast of Bahia (and D. communis furthermore into Pernambuco and Paraíba) .

Drosera tomentosa is one of the most common species of sundews in campos rupestres of Brazil, where it is found in a variety of habitats, often forming large populations. It has been observed growing sympatric with nearly all other Drosera species growing within its geographical range: D. ascendens , D. camporupestris , D. chrysolepis , D. communis , D. graminifolia , D. grantsaui , D. graomogolensis , D. hirtella var. hirtella , D. intermedia , D. latifolia , D. montana , D. riparia , D. spiralis , D. spirocalyx , D. tentaculata , and D. villosa .

Drosera tomentosa prefers growing in sandy-peaty soils around seepages or along streams on islands of vegetation and in cracks on quartzitic rocks. Although it does not usually go dormant in the dry season, growth may slow down and leaves sometimes reduce in size when growing in drier habitats. The largest D. tomentosa specimens are usually found in the wettest soils, sometimes even growing semi-aquatically, while the smaller specimens are often observed in the drier sandy habitats or on bare sandstone surfaces.

Drosera tomentosa is one of the few species of the genus in Brazil that can be found forming healthy populations (albeit less vividly colored) when growing in shaded areas under riparian vegetation, the others being D. communis , D. grantsaui , D. latifolia , D. riparia , and D. viridis .

Previous records of D. tomentosa from São Paulo state ( Silva & Giulietti 1997; Silva 2002) result from a misidentified specimen of D. hirtella var. lutescens [eg. Marcondes-Ferreira et al. 1167 (SPF)].

Drosera tomentosa has been reported to hybridize with D. grantsaui when both species are found sympatrically, often forming large (and possibly fertile) hybrid populations, the hybrid being known as D. × fontinalis Rivadavia (2009: 121). More rarely, D. tomentosa has also been observed to hybridize with D. latifolia and D. villosa ( Gonella et al. 2014) .

Phenology: —Although D. tomentosa may occasionally be found in flower year round, most populations are observed to begin flowering synchronously during the dry season, between June and September, usually lasting for about one or two months (or longer if plants produce two or more scapes).

IUCN Red List Category: — Drosera tomentosa is widespread and abundant across its range, occurring inside several protected areas. It is thus here considered of Least Concern (LC), according to the IUCN criteria ( IUCN 2001).

Discussion: — Drosera tomentosa is distinguished from other members of the complex by its obovate to oblongobovate leaves (rarely oblong), with wide petioles (0.4–3 mm in width), apical tentacles usually inconspicuously distinct in number of 5–9, up to 5 mm long, with a tentacle stalk up to 0.3 mm wide at the base and with a ellipsoid to rectangular-linear gland head up to 0.6 mm long, glandular trichomes absent in the basal third of scape, usually multiple flowered scapes (up to 23 flowers), anthesis in the dry season (June to September), and by the narrowly ovate to oblong-ovate sepals (1.5–3 × 0.6–1.3 mm).

There is great variation in the degree of differentiation of the apical tentacles in D. tomentosa , from almost indistinct (with ellipsoid head) to clearly longer, distinct, and with a rectangular head. However, even when distinct, the apical tentacles of D. tomentosa are always much narrower at the base and have a much shorter head when compared to the large marginal tentacles of D. tentaculata . The D. tomentosa variant with longer and distinct rectangular tentacle heads has been observed growing sympatric with D. tentaculata at the Serra do Cipó and Diamantina regions, raising the hypothesis of hybridization between these species. However, this D. tomentosa variant also occurs vicariantly from D. tentaculata (e.g. in the Serra do Ibitipoca, Serra de São José, and the Chapada dos Veadeiros), suggesting that the larger marginal tentacles of the former may not result from introgression with D. tentaculata , but simply represent natural variation within D. tomentosa .

Although more similar to D. montana or D. tentaculata in most morphological characters, the overall habit of D. tomentosa often significantly resembles diminutive sterile specimens of the taxa in the D. villosa complex (especially D. latifolia ), some of which are known to occasionally hybridize with D. tomentosa ( Gonella et al. 2014) . The floral parts (including seeds) of D. tomentosa var. tomentosa are virtually indistinguishable from those of D. chimaera , however the vegetative parts are very distinct, as the leaves of D. chimaera are narrowly to broadly oblong-lanceolate, semi-erect and completely lack snap tentacles.

Drosera tomentosa is extremely variable in regards to the distribution of eglandular indumentum on the scape and inflorescence, although this character is usually uniform and stable within populations. These white trichomes (pale brown and often deciduous in old or dried specimens) may vary from completely absent to very densely present on entire scapes, from base to apex, including pedicels and sepals.

Plants with scapes displaying a denser eglandular indumentum are more abundant in the northern part of the D. tomentosa range, but variations in scape indumentum are not very continuous geographically. In central Minas Gerais (and more rarely in central Bahia), the morphotype with dense eglandular-pilose indumentum is sometimes found growing sympatrically with the morphotype bearing few or no eglandular trichomes on its scapes – yet both morphotypes remain distinct and easily distinguishable in these populations. This is even evident from the type sheet of D. tomentosa (Saint-Hilaire M-378), which represents a mixed collection of both morphotypes (and even a putative scape of D. latifolia – see Gonella et al. 2014). Artificial crosses between the two morphotypes have been successfully made in cultivation by the authors, and have shown to be fertile. Rarely, intermediate specimens can be observed in mixed wild populations, suggesting that the two morphotypes may also hybridize naturally.

The above observations seem to support the original description by Saint-Hilaire (1826), splitting D. tomentosa into two varieties based on scape eglandular indumentum: D. tomentosa var. tomentosa with hairy scapes and D. tomentosa var. glabrata with glabrous to subglabrous scapes ( Saint-Hilaire 1826). Therefore, in agreement with Saint- Hilaire (1826), two infraspecific taxa are here accepted at the varietal rank, due to the huge overlap in their geographical ranges, possible hybridization, and the fact that the sole distinguishing character (scape eglandular indumentum) is not easily quantifiable. Furthermore, the presence or absence, as well as the density, of eglandular trichomes on scapes of native Brazilian Drosera taxa has caused too much taxonomic confusion in the past, and is also currently known to be a variable character (although to lesser degree) when comparing geographically separated populations of D. cayennensis , D. communis , D. grantsaui , D. latifolia , D. montana , and D. tentaculata . Therefore, any status above rank of variety for the two morphotypes observed in D. tomentosa would require further and more quantifiable data.

Taking into consideration the numerous individuals studied as herbarium specimens and seen in the wild across the range of D. tomentosa , we provide a more detailed treatment of the two varieties below.As the type of D. tomentosa was found to represent a mixed collection of both varieties and possibly D. latifolia , the designation of a lectotype became necessary. Based on the original description by Saint-Hilaire (1826) and a careful examination of the type material, we here select the fifth specimen from the left ( Fig. 14 ) as the lectotype.

Of the three accessions used for cytological studies to determine the chromosome number of D. tomentosa ( Rivadavia 2005) , the vouchers Rivadavia 298 and Rivadavia 449 represent D. tomentosa var. tomentosa , while Rivadavia 439 represents D. tomentosa var. glabrata . Both varieties are tetraploids with 2 n = 40 chromosomes.

Because a clear distinction between D. tomentosa var. tomentosa and D. tomentosa var. glabrata was not always possible for all material studied (either because these contained only sterile specimens, or due to the deciduous nature of the scape indumentum in old herbarium sheets), some of the specimens examined are tentatively listed under D. tomentosa s.l. at the end of the specimen list, without recognition of either variety.

Figures

FIGURE 14. A, type sheet of D. tomentosa, with the selected lectotype highlighted inside a red box; t, D. tomentosa var. tomentosa; g, D. tomentosa var. glabrata; l, D. latifolia. B, detail of the lectotype of D. tomentosa. Image extracted from the Saint-Hilaire Virtual Herbarium (Pignal et al. 2013).