Thismia pseudomelanomitra D.F.Silva & J.M.A.Braga, 2023

Silva, Die- -- Go Fe- -- Rre- -- Ira Da, Ribe- -- Iro, Ricardo Da Silva & Braga, João Marce- -- Lo Alvare- -- Nga, 2023, Thismia pseudomelanomitra (Thismiaceae), a new mycoheterotrophic species from Brazilian Amazon Forest, Phytotaxa 597 (2), pp. 175-183 : 176-181

Thismia pseudomelanomitra D.F.Silva & J.M.A.Braga , sp. nov. ( Figures 1–3 )

Type:— BRAZIL. Mato Grosso: Cotriguaçu, Fazenda S „o Nicolau , Fragmento de Floresta Ombrófila , 09°49’48”S 58°19’14”W, 3 December 2021, fl., D. F. Silva et al. 307 (holotype: RB [dried + spirit]) .

Diagnosis:— Thismia pseudomelanomitra is morphologically similar to T. melanomitra by the inner surface of the floral tube with striated laminar projections, black, and inner tepals connate over the tube opening, forming a black and foveate mitre. However, it differs by the outer tepals ca. 5 × 4–5 mm, orbicular, margin entire, revolute; inner tepals 10–14 mm long., base acute 3–4 mm wide at the point of attachment to the floral tube and connate over the tube opening forming a mitre, black; mitre 8–10 mm in diam., outer surface bearing prominent irregularly dentate ribs and with irregular foveae on top.

Description:—Herbs 11–21 cm tall, terrestrial, mycoheterotrophic, achlorophyllous.Roots 3–4 × ca. 0.2 cm, vermiform, creeping, brownish. Stem 9.5–19 × 0.2–0.3 cm, erect, terete, unbranched, glabrous, white. Leaves 3–11, 1.5–3 × 1.3– 1.5 mm, alternate, scattered along the stem, scale-like, concave, lanceolate, margin entire, apex acute, glabrous, white. Involucral bracts 3–4; bracts 4–5 × ca. 2 mm, lanceolate, concave, margin entire, apex acute, glabrous, white. Flowers 18–22 × 8–11 mm, solitary, actinomorphic, black and white; floral tube 8–10 × 7–8 mm, urceolate, outer surface densely covered with longitudinally arranged irregularly sized verrucae and concentrated from the base to the middle portion of the tube, white, inner surface with striated laminar projections, black; annulus 2–3 mm in diam., hexagonal, colliculate on both surfaces, white. Tepals inserted in two whorls (3+3); outer tepals ca. 5 × 4–5 mm, reflexed, orbicular, giving the false impression of ovate, 1-veined, base acute, margin entire, revolute, apex rounded to obtuse, white; inner tepals 10–14 mm long., spathulate, base acute 3–4 mm wide at the point of attachment to the floral tube, 1-veined, adnate broadening above and connate over the tube opening forming a mitre, black, with three lateral apertures, aperture 3–4 mm in diam., apex of the floral tube not visible through the aperture; mitre 8–10 mm in diam., subglobose; outer surface bearing prominent irregularly dentate ribs and with irregular foveae on top; inner surface colliculate. Stamens 6, ca. 2.3 × 0.8 mm, pendulous, spathulate, glabrous, inserted ca. 3 mm in a rectangular-shaped structure below the annulus, white; interstaminal lobes absent; filaments ca. 0.7 mm long, free; connectives inconspicuous; anthers ca. 1.3 × 0.7 mm, elliptic, apex obtuse. Ovary 4–5 × 4–5 mm, unilocular, top-shaped, plane surface, smooth, glabrous, white, multi-ovulate placentation parietal; style ca. 0.5 mm long, inconspicuous, white; stigma ca. 2 × 2 mm, trilobed and with a central orifice, lobes descendants, auriculate, glabrous, white. Fruits unknown.

Etymology:— The specific epithet is an allusion to the appearance that is falsely similar to T. melanomitra .

Phenology:— Flowering was observed in December.

Distribution and habitat:— Thismia pseudomelanomitra occurs in the Amazon Forest and is known only from the type locality, in the municipality of Cotriguaçu, northwest of the Mato Grosso state, Brazil ( Figure 4 ). The species was found growing on the leaf litter of a Ombrophilous Forest remnant, close to small creeks.According to the K̂ppen classification, the predominant climate is Am, with annual rainfall between 2.800 –3.100 mm and average annual temperature 26ºC ( Alvares et al. 2013).

Conservation status: — Thismia pseudomelanomitra is found in a fragment of Ombrophilous Forest in the northwest of Mato Grosso state. Although the small population is inside a fragment of preserved forest, logging, extensive monoculture, and cattle raising activities were observed in the surrounding area. Due to the low number of individuals and being known from a single locality, it was not possible to estimate the territorial range of the species. Therefore, we suggest that the species is preliminarily maintained as Data Deficient (DD), according to the IUCN criteria (2022).

Morphological affinities: —Following to the classification of Mass et al. (1986), T. pseudomelanomitra belongs to T. subg. Ophiomeris ( Miers 1847: 328) Maas & H.Maas (in Maas et al. 1986: 145) sect. Pyramidalis Maas & H.Maas (in Maas et al. 1986: 161), due to the horizontal cylindrical roots, terete stem with scattered leaves along the stem, pyramidal stigma, stamens with inconspicuous connective, interstaminal lobes absent, and parietal placentation extending from the base to the top of the ovary.

Thismia pseudomelanomitra is morphologically similar to T. melanomitra (see Table 1 , Figure 5 E­­­ –H). However, it differs by the outer tepals orbicular, giving the false impression of ovate, margin revolute (vs. outer tepals ovate, margin plane), inner tepals 10–14 mm long., base 3–4 mm wide at the point of attachment to the floral tube, apex of the floral tube not visible through the aperture, mitre 8–10 mm in diam., subglobose, outer surface bearing prominent irregularly dentate ribs and with irregular foveae on top (vs. inner tepals 7–8 mm long., base ca. 2 mm wide at the point of attachment to the floral tube, apex of the floral tube visible through the aperture, mitre 5–6 mm in diam., hexagonal, outer surface with 6 triangles foveate in top), and by ovary top-shaped, outer surface plane, smooth (vs. oblong, outer surface keeled, verrucose). For a detailed comparison of morphological characters between the species (see Table 1 .)

Figures

FIGURE 1. Thismia pseudomelanomitra. A. Flowering habit. B–C. Leaves. D. Top view of the flower, showing the arrangement of the tepals and foveate mitre. E. Longitudinal section of floral tube with outer and inner tepals, stamens, stigma, placentation and inner surface with striated laminar projections. F. Outer tepals. G. Flower in side view, showing the details of the inner tepals. H. Detail of the stamens, stigma, placentation and inner surface of the floral tube. I. Detail of the inner surface of mitre, colliculate. J. Detail of the inner surface of floral tube with striated laminar projections. Drawing by Marcus Falc„o.

FIGURE 2. Thismia pseudomelanomitra. A. Panoramic view of the area habited by T. pseudomelanomitra. B–F and H. Flowering habit (in situ). G and I. Detail of the mitre, showing the variation in the number of foveae. Photographs by Diego Ferreira da Silva.

FIGURE 3. Thismia pseudomelanomitra. A. Flowering habit. B. Leaves. C. Outer tepals. D. Mitre upper view. E. Detail of the outer surface of floral tube, showing the longitudinally arranged irregularly sized verrucae. F. Longitudinal section of floral tube with outer and inner tepals, stamens, stigma, placentation, and inner surface with striated laminar projections. G. Detail of the inner surface of mitre, colliculate. H. Detail of the annulus. I. Detail of the annulus surface. J. Stamen. K. Stigma and placentation. Photos are provenient of the material in alcohol, disregard coloration. Photographs by Diego Ferreira da Silva.

FIGURE 4. Distribution map of Thismia pseudomelanomitra. A. B. Delimitation of the S„o Nicolau Farm, Cotriguaçu, Mato Grosso, Brazil [satellite images by E­­­ SRI obtained in 2023]. C–D. Habitat of T. pseudomelanomitra.

FIGURE 5. A–D Thismia pseudomelanomitra. A. Flowering habit. B. Detail of the flower, showing the floral tube, outer and inner tepals and top-shaped ovary. C–D. Top view the flower, showing the details of the mitre subglobose and the variation in the number of foveae. E–H Thismia melanomitra. E. Flowering habit. F. Detail of the flower, showing of the floral tube, outer and inner tepals and oblong ovary. G–H. Top view of flower, showing the details of mitre hexagonal, and the variation in the number of foveae. Photos A–D. D.F. Silva 320 (RB), photographs by Diego Ferreira da Silva. E. D.F. Silva & S. Sourell 19 (HE­­­ RBAM), photograph by Susanne Sourell. F–H. D.F. Silva & L.L Mota 03 (HE­­­ RBAM), photograph by Luísa Lima e Mota.