Pinguicula pygmaea Rivadavia, E.L.Read

Rivadavia, Fernando, Read, Edward Lloyd & Fleischmann, Andreas, 2017, Pinguicula pygmaea (Lentibulariaceae), a new annual gypsicolous species from Oaxaca State, Mexico, Phytotaxa 292 (3), pp. 279-286 : 280-283

Pinguicula pygmaea Rivadavia, E.L.Read & A.Fleischm., sp. nov. ( Figs. 1–3 )

Similar to Pinguicula crenatiloba DC. regarding habit, leaf shape, the bilabiate corolla with upper lip smaller than the lower lip, and the overall diminutive size, but differs from that species by entire corolla lobes (crenate to emarginate in P. crenatiloba ), by the upper corolla lip only slightly separated from the lower lip, creating a short tubular throat (deeply bilabiate corolla, tubular corolla throat almost absent), by the three subequal lobes of the lower corolla lip (median lobe much larger than the two lateral ones), and by a spur which exceeds the corolla lower lip in length (spur shorter than to at maximum equal to the length of lower corolla lip).

Type: — MEXICO. Oaxaca: Município de Santo Domingo Tonalá, Highway 125, between Huajuapan and Tlacotepec, 1370 m, 20 November 2003, Rivadavia & Read 1814 (holotype IEB!, isotype M!).

Small delicate annual herb, forming a lax rosette spread flat on the ground. Roots few, poorly developed, unbranched. Active green leaves 2–5, membranous, obovate to elliptic, 4–6(–8) mm long and 2.5–4(–5) mm wide; apex rounded, base cuneate, short petiolate; margins strongly involute in the distal 2/3 of the leaf; lamina upper surface densely covered with short-stalked adhesive and sessile digestive glands. Inflorescences 1-flowered, erect, densely covered with stalked-glands, 1–5(–7) scapes per plant; scapes slightly arcuate and (5–) 10–25 mm long at anthesis, terete, up to 0.5 mm in diameter, straight, erect and prolonged to 30–65 mm in fruit. Calyx pentamerous, bilabiate, densely covered with glandular hairs on the outer surface; the three upper calyx lobes divided to 2/3 of their length, triangular, 1–1.5 mm long and 0.5–1 mm wide; the two lower calyx lobes fused to about 3/4 of their length, c. 2 mm long and 1 mm wide. Corolla pentamerous, bilabiate, tubular, white to very pale rose, white at the base of the corolla lobes near the throat, with yellowish-green mark on the palate at the base of the lower lip and inside the throat and spur; corolla (3–) 3.5–5 mm long including the spur; upper corolla lip bilobate, smaller than the lower lip, lobes spreading, 1–1.5 × 0.5–1 mm, rectangular to ovate-elliptic in outline, apex obtuse to shallowly retuse; lower corolla lip distinctly trilobate, lobes subequal, 1–1.5(–2) mm × 1–1.5 mm, the lateral lobes only slightly smaller than the median lobe, ovate to circular in outline, apex obtuse, palate sparsely covered with short, subclavate to cylindrical, multicellular hairs c. 0.05–0.1 mm long; tubular throat widely open, very short, 0.5–0.7 mm long, up to 7 mm in diameter, conical to cylindrical; spur yellowish-green, narrowly conical to cylindrical, narrowed towards an acute or obtuse apex, 1–2.5(–3) mm long, 0.3–0.5 mm in diameter; corolla outer surface glabrous, except single scattered glandular hairs on the spur. Anthers 2, filaments falcate, white, c. 0.7 mm long and up to 0.2 mm wide, papillate, thecae subequal. Ovary subglobose, glandular; style short, subsessile, c. 0.5 mm long, stigma bilabiate, the lobes subequal, upper lobe scale like, c. 0.1 mm long, the lower lip much larger, c. 0.4 mm long, suborbicular, papillate, reddish pink. Capsule globose, to 1.5 mm in diameter, subequaling the persistent calyx lobes, wall membranous, capsule longitudinally bivalvate. Seeds numerous, light brown, truncate-obovoid, testa reticulate.

Distribution: — Pinguicula pygmaea is known from only two localities just south of Santo Domingo Tonalá (c. 1370–1400 m elevation) and one just north of Santiago Juxtlahuaca (c. 1680 m elevation), along highway 125 between Huajuapan and Tlacotepec, in western Oaxaca state, Mexico. Although no further populations of P. pygmaea have been discovered (or specifically searched for) so far, it is likely that the species occurs in at least some of the numerous seemingly suitable habitats on gypsum hillsides observed in the vicinities of Tonalá and Juxtlahuaca ( Fig. 2 ).

Conservation status:—Although very abundant at two of the three sites where it was observed, P. pygmaea does not occur within any protected area, and it is not guaranteed to occur in other apparently suitable habitats nearby. Moreover, easily accessible gypsum deposits are generally under potential threat from mining (IUCN Threats Classification: 3.2). Therefore, this new species is considered Vulnerable (VU D2) according to the criteria of IUCN (2012).

Etymology: — The specific epithet “ pygmaea ” (pygmy) denotes the minute size of this delicate annual, which is among the smallest of all known Pinguicula species, only rivaled in its diminutive stature by the closely related P. crenatiloba , as well as by the only distantly related, Arctic circumpolar perennial Pinguicula villosa Linnaeus (1753: 17) and dwarf specimens of the annual Pinguicula lusitanica Linnaeus (1753: 17) from Atlantic western Europe and north-western Africa.

Habitat and ecology:—Annual therophyte and strictly gypsicolous. Pinguicula pygmaea grows on north-facing gypsum walls and hillsides in xeric shrubland, accompanied by the poikilohydric perennial (“resurrection plant”) Selaginella L., the perennial heterophyllous geophyte Pinguicula heterophylla Bentham (1840: 70) , annuals such as Centaurium Hill ( Gentianaceae ), and xerophytic and geophytic perennial plants such as species of Hechtia Klotzsch ( Bromeliaceae ), Agave L. ( Agavaceae ), Oxalis L. ( Oxalidaceae ), Aristolochia L. ( Aristolochiaceae ), Opuntia Mill. , Neobuxbaumia mezcalaensis (Bravo) Backeb. ( Cactaceae ), Fouquieria ochoterenae Miranda ( Fouquieriaceae ), Brahea dulcis (Kunth) Mart. ( Arecaceae ), ferns, liverworts, and grasses. Pinguicula pygmaea is locally abundant at two of the three sites studied in early and late November on north-facing hillsides, growing in open gypsum soil. At the third site, only a small number of individuals was observed. At two of the three sites, P. pygmaea grows sympatrically with P. heterophylla . The type location was revisited in December 2003, three weeks after the species’ initial discovery, and almost all plants were already dead, possibly as a result of a frost event that occurred the night before, but not because of drought. The remaining annual species in Mexico ( P. lilacina , P. crenatiloba , and P. takakii ) have been observed alive and flowering well into the dry season at some locations (information from herbarium records, and from R. Resendiz Torreblanca, pers. comm.), as late as February. This suggests that, unlike P. pygmaea , these other species are seemingly unaffected by the light frosts of winter. It is suspected that cooler winter temperatures often allow these annuals to persist into the mid or late dry season thanks to a combination of condensation at night and shade resulting from the northern orientation of their habitats or from surrounding vegetation. Moreover, at least in the state of Oaxaca, P. lilacina and P. crenatiloba appear to occur at lower elevations (250–1000 m, see other specimens examined in Appendix 1 and Fig. 2 ) compared to P. pygmaea (1370–1680 m), hence will experience different climatic conditions. However, P. lilacina , P. crenatiloba and P. takakii apparently die off as the weather heats up and soils dry out late in the dry season, when the sun rises higher during spring (March to June), and before the rains return in late spring and early summer (June to July). The Sierra Madre del Sur highlands of southern Mexico (Oaxaca, Guerrero and southern Michoacán) is rich in Pinguicula species, especially on its eastern portion in the state of Oaxaca. The high species diversity of Pinguicula (and also other species-rich montane plant genera) observed on certain Mexican mountain ranges has been explained by differing microclimates and especially a variety of edaphic conditions found in close proximity, ranging from limestone and gypsum to igneous and volcanic rock, resulting in many geographically close but fundamentally different habitat niches ( Zamudio 2005, Mastretta-Yanes et al. 2015). Among the Mexican mountain ranges, the Sierra Madre del Sur is geomorphologically the most complex, with a marked topography resulting in a mosaic of soils and climatic gradients ( Krasilnikov et al. 2011). Yet, no gypsum endemic Pinguicula species (following the species concept of Lampard et al. 2016) was known thus far from the Sierra Madre del Sur before the discovery of P. pygmaea —in contrast to the Sierra Madre Oriental of north-eastern Mexico (Coahuila, Nuevo Léon, Tamaulipas, San Luis Potosí, Hidalgo, to northern Puebla and Querétaro states), likewise a Pinguicula diversity center providing various soil types, including gypsum, that host six narrowly endemic gypsicolous species: P. debbertiana Speta & Fuchs (1992: 375) , Pinguicula gypsicola Brandegee (1911: 190) , Pinguicula immaculata Zamudio & Lux (1992: 40) , Pinguicula nivalis Luhrs & Lampard (2006: 4) , Pinguicula rotundiflora Studnička (1985: 201) and P. takakii ( Zamudio & Lux 1992, Zamudio 2005, Lampard et al. 2016).

Taxonomic relationships:— Pinguicula pygmaea is closely related to P. crenatiloba , a delicate annual species, with which it shares leaves with strongly involute margins (incurved up to 1 mm) in the apical 2/3 of the lamina, calyx shape, and especially the bilabiate corolla with very short and only weakly pronounced tubular throat. However, the former species is readily distinguished from the latter by its corolla, which has subequal lobes with an entire margin and an obtuse to shallowly retuse apex. The corolla lobes of P. crenatiloba differ greatly between the upper and lower lip: the lobes of the corolla upper lip are distinctly smaller, more or less rectangular in outline, with bifid apex and acute (rarely obtuse) tips, while the lobes of the corolla lower lip are much larger, with undulate (rarely rotundate) to emarginate apex. In contrast to the strict gypsicole P. pygmaea , the closely related P. crenatiloba , and the likewise delicate annual P. lilacina (which is of different corolla shape, see Table 1 and Fig. 3 ) do not occur on gypsum soil, but inhabit clayey soils overlying limestone or igneous rock ( Casper 1966, Zamudio 2005).

The delicate habit and the corolla entire lobes and color of P. pygmaea are superficially similar to the also annual P. takakii (see Table 1 and Fig. 3 ), which inhabits similar gypsum soils of the Sierra Madre Oriental in San Luís Potosí state, north-eastern Mexico, often sympatric with P. gypsicola .

herbarium specimens and from literature ( Ernst 1961, Casper 1966, Zamudio & Rzedowski 1986, Lampard et al. 2016).

Other specimens examined (paratypes): — MEXICO. Oaxaca: Município de Tonala: Highway 125, between Huajuapan and Tlacotepec, 1 km south of Tonalá , c. 1380 m alt., 5 November 2016, F. Rivadavia, R. Resendiz Torreblanca, J. I. Guerrero Argüelles, A. Pérez Ángeles & J. Gomez Landeros 2726 ( XAL!) ; Highway 125, between Huajuapan and Tlacotepec, 3 km south of Tonalá , c. 1400 m alt., 5 November 2016, F. Rivadavia, R. Resendiz Torreblanca, J. I. Guerrero Argüelles, A. Pérez Ángeles & J. Gomez Landeros 2727 ( XAL!) ; Município de Tlacotepec : on hills next to the Laguna Encantada, c. 1680 m alt., 5 November 2016, F. Rivadavia, R. Resendiz Torreblanca, J. I. Guerrero Argüelles, A. Pérez Ángeles & J. Gomez Landeros 2728 ( XAL!) .

Figures

FIGURE 1. Pinguicula pygmaea. A, habit (left: specimen near the end of its growing cycle; right: specimen at the beginning of anthesis). B, leaf. C, corolla, side view. D, corolla, face view. E, corolla, flower preparation (spur dissected from the corolla). F, multiseriate hairs from corolla palate. G, calyx. H, seed. A, B, G, H from Rivadavia & Read 1814, E, F from Rivadavia et al. 2727, C, D from photographs of plants in situ. Drawing by A. Fleischmann.

FIGURE 2. Distribution of Pinguicula pygmaea (white stars), of the related P. crenatiloba (white boxes), and the similarly annual P. lilacina (black dots) in southern Mexico (location data based on herbarium records and field observations). The fourth small Mexican annual species, P. takakii, is endemic to San Luis Potosí state, which is outside the range of this map.

FIGURE 3. Morphological comparison between Pinguicula pygmaea, P. crenatiloba, P. lilacina and P. takakii. All scale bars = 5 mm. Photos by F. Rivadavia, except P. crenatiloba middle row and lower row right top image, P. lilacina middle and lower row (by R. Resendiz Torreblanca) and P. crenatiloba lower row left image (by M. Welge).