Paepalanthus modestus Trovó, 2017

Trovó, Marcelo, Silva, Arthur De Lima & Coan, Alessandra Ike, 2017, Paepalanthus modestus (Eriocaulaceae), a new dimerous species from Goiás, Brazil, with notes on leaf and scape anatomy, Phytotaxa 316 (3), pp. 271-278 : 272-277

Paepalanthus modestus Trovó , sp. nov. Figs. 1 & 2 .

Paepalanthus modestus differs from Paepalanthus harleyi by its smaller habit, longer leaves (vs. short) with tufted leaf apex (vs. glabrous), greenish to pale straw-colored spathes (vs. dark brown), shorter and tightly adpressed trichomes covering the scapes (vs. long, loose trichomes), involucral bracts only slightly surpassing the floral disc (vs. conspicuously surpassing), hemispherical capitula when mature (vs. discoid), navicular sepal of the staminate flower (vs. obovate), and pedicellate pistillate flower (vs. sessile).

Type:— BRAZIL. Goiás: Alto Paraíso de Goiás, Parque Nacional da Chapada dos Veadeiros. Arredores da cidade na beira da estrada para Cavalcante, 12 March 2015, M. L. O. Trovó & A. L. Silva 646 (holotype RB; isotypes B, NY, P, SPF, UB) .

Cespitose herbs, usually forming small clumps, ca. 15.0−30.0 cm tall; rhizome present, usually sprouting, aerial stem short ca. 1.0 cm long. Leaves deciduous, restricted to the leaf sheath at the aerial stem base, 5.0−15.0 × 0.05−0.1 cm, greenish to pale straw-colored, chartaceous, linear, erect, sometimes twisted, sparsely pilose with long trichomes to glabrescent, margins glabrescent, apex acute, tufted to glabrescent. Spathes 2.5−5.0 cm long, greenish to pale straw-colored, glabrescent, apex acute. Scapes usually terminal and solitary at the ramet stem apex, 14.0−29.0 cm long, covered with tightly adpressed trichomes, rarely with long, patent trichomes or glabrescent. Capitula ca. 3−8 mm diam., hemispherical when mature, whitish; involucral bracts in 2−4 series, ca. 1.5 mm long, slightly surpassing the floral disc, castaneous, ovate to deltoid, flat, pilose to glabrescent at the abaxial surface, margin densely ciliate, apex acute to acuminate; receptacle flat. Flowers dimerous, ca. 70 per capitulum, ca. 40 staminate and 30 pistillate; floral bracts ca. 2.5 mm long, castaneous, linear, glabrous, margin glabrous, apex acuminate, tufted. Staminate flowers ca. 2.5 mm long; pedicel ca. 0.5 mm long; sepals free, ca. 2.0 mm long, navicular, castaneous, pilose at the top of the abaxial surface, margin ciliate toward the apex, apex obtuse, tufted; anthophore fleshy, elongated; corolla fused in a tube, ca. 0.5 mm long, whitish, membranaceous; stamens ca. 0.8 mm long; carpellodes 2, papillose. Pistillate flower ca. 2.5 mm long, pedicel ca. 0.5 mm long; sepals free, ca. 2 mm long, obovate, castaneous, pilose at the abaxial surface, margin ciliate toward the apex, apex acute, tufted; petals ca. 2 mm long, elliptical, light castaneous, margin ciliate toward the apex, apex acute, tufted; gynoecium ca. 1.5 mm long, stigmatic branches bifid at the apex, of the same size as the nectariferous branches. Fruit a loculicidal capsule. Seeds elliptical, brown to reddish.

Etymology: —The epithet “ modestus ”, meaning small-sized, refers to the habit of the new species compared to the other Brazilian species of Paepalanthus [unranked] Dimeri.

Distribution, Habitat, and Conservation: — Paepalanthus modestus is restricted to the state of Goiás, Brazil, in the vicinities of the Chapada dos Veadeiros, with populations known in the neighboring municipalities of Alto Paraíso de Goiás and Teresina de Goiás ( Fig. 2A ). The species grows in rocky sandy-argillaceous soils, usually forming large populations of hundreds of individuals. Most of the collections come from both sides of the GO-118 highway, some of them inside the Chapada dos Veadeiros National Park. Based on the species distribution, it is considered endangered according to the IUCN (2011) criteria B1ab (i,ii,iii,iv).

Additional specimens examined: — BRAZIL. Goiás: Alto Paraíso de Goiás, 20 February 1975, Hatschbach et al. 36349 ( MBM, MO) ; 10 January 1991, Giulietti 1085 ( SPF) ; 06 May 2002, Magenta et al. 450 ( SPF) ; 25 September 2011, Forzza et al. 6764 ( RB) ; 13 March 2015, Trovó & Silva 648 ( RB, SPF, UB). Teresina de Goiás, 01 December 1992, Hatschbach et al. 58364 ( MBM, MO, NY) ; 13 March 2007, Pastore et al. 1837 ( CEN, HUEFS, K) .

Comments:— The new species is placed in Paepalanthus [unranked] Dimeri due to its dimerous flowers, short stem, bifid stigmatic branches, and flat receptacle. Its cespitose habit forming small clumps of sprouting ramets each bearing a single terminal capitulum and its linear leaves also approximate P. modestus to other species of this group, and to the P. elongatus complex. However, the hemispherical capitula when mature, the relatively short involucral bracts only slightly surpassing the capitula, along with the vestiture of leaves and scapes distinguish P. modestus as a unique taxon.

Paepalanthus modestus shares a general habit with P. harleyi , a species restricted to the slopes of the Pico das Almas (Bahia) and with P. oxyphyllus , a species known only from the type specimen collected in Minas Gerais. From the former species, P. modestus is segregated by its usually smaller habit and tufted leaf apex, longer leaves, greenish to pale straw-colored spathes, tightly adpressed trichomes covering the scapes, hemispherical capitula, involucral bracts only slightly surpassing the floral disc, navicular sepal of the staminate flower, and pedicellate pistillate flower (Tab.1). Paepalanthus modestus is easily distinguished from P. oxyphyllus by its smaller habit, usually tufted leaf apex, scapes densely covered by trichomes, hemispherical capitula when mature, the pilose involucral bracts slightly surpassing the floral disc, and the pedicellate staminate flower (Table 1).

TABLE L. Morphological comparison of Paepalanthus modestus , P. oxyphyllus , and P. harleyi . Features for P. oxyphyllus and P. harleyi are cited from Koernicke (1863), Ruhland (1903), Moldenke (1980), and Giulietti & Parra (1995).

Fire is a rather common event in the Chapada dos Veadeiros region. Large populations of Paepalanthus modestus were observed in flower shortly after fire events (Trovó unpublished data, Forzza personal communication), and some of the herbarium specimens were also collected after fire events, as noted on the specimens and labels (e.g. Forzza et al. 6764– RB). Therefore, fire may promote blooming in this species; this hypothesis requires testing. The subterranean rhizome and the aerial stem covered by leaf sheaths ( Fig. 2B ) may act as protection against fire, because the leaves and the leaf sheaths seem to burn ( Fig. 2C ) but the individuals survive, sprouting from the rhizome.

Unusual growth of the involucral bracts ( Fig. 2K ) was observed in some individuals of Paepalanthus modestus in the field and in some herbarium specimens (e.g. Trovó & Silva 646 –SPF, UB). These bracts are not only unusually long but are also of different shape and vestiture. Such abnormal bract formation should be better studied and characterized. Some of the taxa described for P. [unranked] Dimeri are only differentiated by bract morphology and may, in fact, only represent teratogenic forms of the same species.

Anatomical Notes:— Leaves of P. modestus have a single-layered epidermis covered with thin cuticle ( Fig. 3A ). Epidermal cells are longitudinally elongated in frontal view ( Fig. 3B ), and small and isodiametric in cross section ( Fig. 3A and C ). On the adaxial surface, cells have slightly thickened walls, while on the abaxial surface and on leaf margins, cells have thickened walls ( Fig. 3A ). Trichomes (tr) are found sparsely on both surfaces and on leaf margins ( Fig. 3A ). Leaves are hypostomatic, with paracytic stomata (st) ( Fig. 3B ) located slightly above the other epidermal cells and displaying regular substomatal chambers (c) ( Fig. 3C ). The mesophyll consists of an adaxial hypodermis (hp) formed by 3–4 layers of large rounded cells with slightly thickened walls ( Fig. 3A ); a central region of compact chlorenchyma (*) ( Fig. 3A and C ); and 2–3 layers of sclerenchymatous cells adjacent to the abaxial epidermal surface ( Fig. 3A and C ). The vascular tissue consists of five large vascular bundles with bundle sheath extensions (se) ( Fig. 3D ); two small vascular bundles adjacent to the large central bundle and attached to the hypodermis; and two small vascular bundles close to the leaf margins ( Fig. 3A ). All vascular bundles are collateral and surrounded by a double sheath: the outer one (os) is formed by large, thin-walled cells and the inner one (is) is formed by small, thick-walled cells ( Fig. 3D ).

Scapes of P. modestus are 5-costate and consist of epidermis, cortex and vascular cylinder ( Fig. 3E ). The epidermis is single-layered and formed by small, thick-walled cells and sparsely distributed trichomes (tr) ( Fig. 3E ). Stomata (st) are located slightly above the other epidermal cells and are restricted to the intercostal regions ( Fig. 3E ). The cortex has five regions of sclerenchyma (sc) that alternate with five regions of chlorenchyma (*) ( Fig. 3E ). The endodermis (en) is discontinuous, single-layered and formed by thin-walled cells, forming a cap over the outer bundles of the vascular cylinder ( Fig. 3E ). The pericycle (pe) is stellate, formed by thick-walled cells, completely surrounding the outer bundles and partially surrounding the inner ones ( Fig. 3E ). The pith is conspicuous, formed by large cells with slightly thickened walls ( Fig. 3E ).

Anatomical features of leaves and scapes of P. modestus — such as epidermis with thick-walled cells, compact chlorenchyma, well developed sclerenchymatous tissue, and stomata slightly above the level of other epidermal cells—show adaptations to the xerophytic environment where the species occurs, and are very common features in other Eriocaulaceae species ( Scatena & Rosa 2001, Oriani et al. 2005, Trovó et al. 2010). In comparison to other dimerous species of Paepalanthus already studied ( Scatena et al. 2005, Alves et al. 2013, Trovó et al. 2015), leaves of P. modestus can be distinguished by the presence of epidermis with small, thick-walled cells and sclerified cells under the abaxial epidermal surface. The anatomy of the scape is very similar to those found in P. sect. Diphyomene (1903: 184), especially due to the large number of ribs and the conspicuous pith in the central cylinder ( Trovó et al. 2010, Alves et al. 2013).

Figures

FIGURE 1. Holotype of Paepalanthus modestus collected in Alto Paraíso de Goiás (Goiás–Brazil) (M.L.O. Trovó & A.L. Silva 646– RB).

FIGURE 2. Paepalanthus modestus. A. Habitat. B. Stem and rosette before fire. C. Stem and rosette after fire. D. Leaf apex. E. Spathe detail. F. Spathe detail. G. Young scape detail. H. Old scape detail. I. Mature capitulum. J. Young capitulum highlighting the involucral bracts. K. Capitulum with abnormal involucral bracts. L. Floral bract abaxial surface. M. Staminate flower. N. Pistillate flower. O. Gynoecium. P. Fruit releasing the seeds. (M.L.O. Trovó & A.L. Silva 646–RB).

FIGURE 3. Anatomical sections of leaves and scapes of Paepalanthus modestus (M.L.O. Trovó & A.L. Silva 646–RB). A. Transverse section of the leaf. B. Paradermal view of the abaxial leaf surface. C. Detail of the abaxial leaf surface. D. Detail of a vascular bundle. E. Transverse section of the scape. (Scale bars:A, E= 200μm; B–D= 50μm).