Stigmatodon enigmaticus D.R. Couto, Gonella & A.F. Costa, 2023

Couto, Dayvid R., Gonella, Paulo M. & Costa, Andrea F., 2023, Stigmatodon enigmaticus (Bromeliaceae, Tillandsioideae), a new lithophytic species from the Campos Rupestres within the Brazilian Atlantic Forest, Phytotaxa 584 (3), pp. 207-215 : 209-212

Stigmatodon enigmaticus D.R. Couto, Gonella & A.F. Costa , sp. nov. ( Figures 1–2 )

Stigmatodon enigmaticus differs from S. vexatus by the more numerous leaves (15–25 vs. 10–12 in number), distinctly smaller leaf blade (6–8.5 × 1.5–2.3 cm vs. 13–14 × 2.8–3.7 cm), with acuminate apex (vs. caudate), floral bracts red (vs. green), flowers with diurnal anthesis (vs. nocturnal), greenish-yellow sepals (vs. green), yellow petals (vs. greenish-yellow), and stamens and stigma exceeding the corolla (vs. shorter than the corolla).

Type: — BRAZIL. Minas Gerais: Conselheiro Pena, Serra do Padre Ângelo, Serra do Pinh „o, campo rupestre, 1,300 m elevation, 2 May 2021 (flowered in cultivation in November 2021), P . M . Gonella 2965, D. P . Cordeiro , G . A . da Silva , P . R . Bartholomay , J . C . Ribeiro & L . Medeiros (holotype MBML!) .

Description: — Plant rupicolous, heliophytic, 21–35.5 cm tall when flowering, propagating by basal axillary shoots. Leaves 15–25, forming a utriculiform rosette; sheath ovate to elliptic, 6–8.5 × 4–5.5 cm, purplish to purplishgreen distally, castaneous at the base, densely lepidote on both sides, chartaceous; blade narrowly triangular, 6–8.5 cm long, 1.5–2.3 cm wide at the base, green to dark reddish, densely lepidote on both sides, forming white crossbands on adaxial surface, suberect to spreading-recurved, revolute along the margins (under water stress), apex acuminate. Peduncle suberect or curved at the base, (16-) 23–30 cm long, 1.2–1.8 mm in diameter, green, glabrous; peduncle bracts erect, exceeding the internodes, imbricate, elliptic, apex rounded then acuminate to caudate, 1.7–3 × 1.4 cm, the lower ones subfoliaceous, green, the upper ones red, lepidote on both sides, more sparsely lepidote near the margins, densely white lepidote near the apex. Inflorescence simple, 4–12 cm long, suberect, with apical sterile bracts, 3–7 flowered; main axis slightly geniculate, 2.8–3 mm in diameter, green, glabrous, internodes 5–9(-16) mm; floral bracts suborbicular, apex broadly obtuse, 1.7–2.2 × 1.0– 1.7 cm, ecarinate, secund with the flowers at anthesis, red, exceeded by the sepals, densely lepidote abaxially, adaxially glabrous, coriaceous. Flowers distichous, secund at anthesis, diurnal, 4.0– 5.5 cm long; pedicel green, 4.5–7.2 mm long; sepals elliptic, apex obtuse, 20–23 × 10–11 mm, greenishyellow, ecarinate, glabrous, coriaceous, free; petals linear-oblong, 3.0–3.5 × 0.5–0.8 cm, apex rounded to emarginate, suberect with spreading apex, yellow, glabrous, connate at the base to 0.9–1.5 mm, forming a prevailing tubular corolla; petal appendages 6–7.6 × 2–2.5 mm, spatulate, apex rounded, distally free for 2.5–3.2 mm; stamens exserted for 2–3.8 mm; anthers oblong in outline, 4–5 mm long, obtuse, dorsifixed near the base; filaments complanate, 25–31 mm long, pale yellow, adnate to the petals for 4.3–5 mm; ovary superior, 4.2–5.4 mm long; style 30–35 mm long; stigma convolute blade type (the vriseoid type II), exceeding the corolla for 8–9 mm, green, ca. 1.4 mm in diameter. Capsules unknown.

Phenology: —Colected with flowers in October (in situ), and in November and December (in cultivation).

Distribution and ecology: — Stigmatodon enigmaticus is a lithophyte on quartzitic rocky outcrops ( Fig. 1C ) within the Atlantic Forest, in the municipality of Conselheiro Pena, eastern Minas Gerais state, Brazil. So far, the species is only known from the type locality at Serra do Pinh„o (above 1,250 m elevation), part of Serra do Padre Ângelo ( Fig. 1A ). At the type locality, the species forms a small and sparse population, exposed to full sunlight, growing in crevices or fissures, or directly on bare rock, usually on horizontal or inclined quartzitic rocky outcrops ( Fig. 1 ), surrounded by herbaceous and shrubby vegetation ( Fig. 1B, C ). The floral characteristics of this species, i.e., floral bracts red, flowers with diurnal anthesis, yellow petals, and stamens and stigma exceeding the corolla ( Fig. 1F–H ), allows us to suggest that it is possibly pollinated by hummingbirds ( Neves et al. 2020), an unusual characteristic for the genus Stigmatodon (its species have nocturnal flowers and bat-pollination). This observation raises new and promising perspectives for evolutionary, morphological, and taxonomic studies in Stigmatodon .

Preliminary conservation status: —Critically Endangered (CR): B2ab(iii). Stigmatodon enigmaticus is a microendemic species with an Area of Occupancy (AOO) of 4 km ², found only in Serra do Pinh„o ( Fig. 1 A–B ). While the rock outcrop where it is found is relatively protected from fires by the irregular topography, the surroundings have been severely transformed in the past decades, from the original matrix of Semideciduous Seasonal Forest to pastures for cattle farming. Fires for pasture renovation are regular in the area, as is the active conversion of the few remnants of secondary forest into pastures, with the use of fire, one of such observed during one of the expeditions to the area in October 2022. Similar criminal fires resulted in a wildfire of great proportions that affected the neighboring Pico do Padre Ângelo in September 2020, affecting many of its endemics ( Andrino & Gonella 2021, Kollmann & Gonella 2021, Gonella et al. 2022). The frequent fires in the area facilitated the invasion of the rocky outcrops by alien grass species, such as Melinis minutiflora Beauvois (1812: 54) , which can be found on the rocky outcrop that S. enigmaticus inhabits. The area where the species is found is not protected by any sort of Protected Area but should be recognized as a priority for conservation given the exceptional biodiversity and the relevance of the ecosystem services provided by the mountainous relief and native vegetation of Serra do Padre Ângelo, such as water cycle, climate balance, and pollinators, among others. Finally, less than 20 mature individuals could be located in the area, suggesting that the population is relatively small, as is common with microendemic species from the Campos Rupestres (Conceiç„o et al. 2007). Given the aforementioned characteristics and threats, we have preliminarily assessed S. enigmaticus as Critically Endangered based on the categories and criteria of IUCN (2012).

Etymology: — This new species was discovered in May 2021, when only sterile specimens were observed, and its vegetative characteristics pointed to Stigmatodon . However, when in flower, its red bracts and yellow sepals and petals, common in Vriesea and so far not reported for Stigmatodon , raised the question of its generic placement. This puzzling combination inspired the epithet, from the Greek aenigma meaning “riddle”, or “enigma”.

Additional specimens examined (paratypes): ___ BRAZIL. Minas Gerais: Conselheiro Pena, Serra do Padre Ângelo, Serra do Sossego , campo rupestre, 1,250 m elevation, 15 October 2022, (fl.), D. R. Couto 6625, P. M. Gonella, L. Medeiros, D. Cordeiro & L. Magalhães ( R!); ibidem, 1,350 m elevation, 13 May 2022, P. M. Gonella 3521, E. P. Fernandez, G. Crispin, G. A. Queiroz & J. C. Ribeiro ( MBML!) .

Discussion: — Stigmatodon enigmaticus , resembles the small rupicolous species of “ Stigmatodon limae group” ( Fig. 1 C ), from which it is easily distinguished by its red floral bracts, as well as by the yellow and linear-oblong petals, and the exserted stamens and stigma.

Among the species of the S. limae group, this new species is morphologically most similar to S. vexatus , which is endemic to the Pico da Aliança, an emblematic quartzitic mountain distant about 20 km from the type locality of S. enigmaticus , in the neigboring municipality of Alvarenga. Stigmatodon enigmaticus can be distinguished from S. vexatus by its ovate to elliptic leaf sheaths (vs. broadly ovate), which are purplish to purplish-green toward the apex and castaneous at the base (vs. vinaceous brown adaxially), leaf blade with revolute margins (under water stress vs. flat to involute), peduncle longer (up to 30 cm vs. up to 13 cm), larger flowers (4.0– 5.5 cm vs. ca. 3.2 cm), and obovate to elliptic sepals (vs. oblong-elliptic; data on S. vexatus from Leme 2016).

For the Stigmatodon limae group, three stigma types have been recognized recently (see Leme et al. 2022a), which are relevant to the Stigmatodon taxonomy: tubo-laciniate type II, observed in S. rosulatulus ( Leme 2012: 10) Leme, G.K. Br. & Barfuss (in Barfuss et al. 2016: 58) and S. ilhanus Leme & D.R. Couto (in Leme et al. 2022a: 7); (ii) convolute-blade (the vriseoid type II), observed in S. freicanecanus (Siqueira & Leme, 2006a: 377) D.R.Couto & A.F.Costa (in Couto et al. 2022: 352), S. oliganthus ( Baker, 1887: 345) D.R.Couto & A.F.Costa (in Couto et al. 2022: 354), S. vellozicolus (Leme & Siqueira 2006b: 406) D.R.Couto & A.F.Costa (in Couto et al. 2022: 354), S. vexatus and S. enigmaticus ; and (iii) convolute-blade type III (stigmadontoid type III), observed in S. andaraiensis ( Leme 2012: 16) D.R.Couto & A.F.Costa (in Couto et al. 2022: 352), S. itamarajuensis Leme, D.R. Couto & L. Kollmann (in Leme et al. 2022a: 9), S. limae ( Smith 1970: 181) D.R.Couto & A.F.Costa (in Couto et al. 2022: 354), and S. zonatus (Siqueira & Leme 2006a: 374) D.R.Couto & A.F.Costa (in Couto et al. 2022: 354).

The floral features of S. enigmaticus , i.e., red bracts and yellow perianth, exserted stamens and stigma, and diurnal anthesis, are unique in the genus Stigmatodon but common in Vriesea ( Costa et al. 2014, Neves et al. 2020, Couto et al. 2022). These characteristics, associated with hummingbird pollination syndrome (ornithophily), seem to be the ancestral state among bromeliads, while bat pollination (chiropterophily) originated multiple times in the family as a whole ( Aguillar-Rodríguez et al. 2019), as well as in Vriesea ( Kessler et al. 2020; Neves et al. 2020), and is supported as an ancestral state in Stigmatodon species ( Couto et al. 2022). All the 33 previously known species of Stigmatodon bear chiropterophilous flowers, therefore the floral features of S. enigmaticus could result from the retention of the ancestral state or a reversion to it, a hypothesis that needs to be tested with molecular phylogeny.

Figures

FIGURE 1. Stigmatodon enigmaticus. A. General view of the landscape of campos rupestres and forests at type locality at Serra do Pinh„o, part of Serra do Padre Ângelo (Conselheiro Pena, MG). B. Quartzitic rocky outcrops, habitat of S. enigmaticus. C. Habit of S. enigmaticus. D. Flowering specimen of S. enigmaticus (specimen Couto et al. 6625, paratype). E. Detail of leaves and bracts of the base of the inflorescence. F. Side view of the inflorescence of a cultivated specimen (specimen Gonella et al. 2965, holotype), showing the red bracts and yellow perianth. G. Lateral view of the flower. H. Front view of the flower, showing the position of stamens and stigma. (Photos: A–C, E, G, H by PMG; F by DRC; D by Lucian Medeiros).

FIGURE 2. Stigmatodon enigmaticus. A. Habit. B. Leaf. C. Peduncle bract. D. Floral bract, adaxial surface. E. Floral bract, abaxial surface. F. Flower. G. Sepal. H. Petals, stamens and appendages at the base. I. Details of basal petal appendages. J. Filament and anther. K. Pistil. Drawing by Joelcio Freitas based on the holotype P.M. Gonella 2965 (MBML).