Tridimeris huatuscoana Marinero-Sobal & Ortiz-Rodr., 2022

Rodríguez, Andrés Ernesto Ortiz & Marinero-Sobal, Esteban José, 2022, Fog and coffee: a new species of Tridimeris (Annonaceae) endemic to the mountain cloud forest of Mexico, Phytotaxa 548 (2), pp. 146-152 : 147-151

Tridimeris huatuscoana Marinero-Sobal & Ortiz-Rodr. sp. nov. ( Figs. 1–3 , Table 1 ).

Type:— MEXICO. Veracruz, Huatusco, Río seco, road between Ixpila and Huatusco on the way to Tenejapa , approximately 3 km south of Huatusco , 19.127376° N, 96.981851° W, 1283 m, montane cloud forest, tree 7 m tall, cream-white flowers, in riparian vegetation within the montane cloud forest, 2 January 2022, E. J . Marinero-Sobal 425 (holotype MEXU!, isotypes CIB!, MO!) .

Similar to Tridimeris chiapensis in its glabrous fruit surface and flowers with food bodies at the base of the inner petals, but differing from this species by its setose leaf domatia, longer and pubescent cream-white petals, greater number of flowers per inflorescence, fewer carpels per flower, and by its shorter pedicels.

Tree 5–7 m tall and 3–14 cm in diameter; young branches slightly pubescent, trichomes appressed and golden-brown in color, very soon glabrous. Leaves membranaceous to chartaceous, alternate, phyllotaxy distichous, 7–17 cm long to 2.5–5.5 wide, narrowly elliptic to obovate, apex acute to long acuminate, base acute to obtuse, sometimes slightly asymmetrical; upper and lower surface glabrous; venation eucamptodromous to weakly brochidodromous, 6–9 secondary veins per side, pocket domatia in the axils of the main veins, setaceous; midrib impressed above and slightly canaliculate toward the base, lateral veins impressed above; midrib and lateral veins prominently elevated below and with very sparsely and appressed light-brown hairs, lateral veins decurrent at midrib insertion; petiole swollen and blackish when dry, 0.3–0.6 cm long, canaliculate, with sparsely and appressed light-brown hairs. Inflorescences axillary, 2-flowered short shoots (rhipidia), flowers develop in succession, sympodial axis minute, 0.1–0.2 cm long, densely golden-brown tomentose. Flowers almost sessile, pedicels 0.1–0.3 cm long (up to 0.5 cm in fruit), densely covered by appressed golden-brown trichomes and bearing 2–3 minute, densely golden tomentose and broadly ovate basal bracts. Sepals 2, connate, 0.2–0.3 cm long × 0.2–0.3 cm wide, decurrent along the pedicel, broadly ovate to orbicular, rounded at apex, sparsely to densely covered by appressed golden-brown trichomes outside, glabrous inside, margins ciliate. Petals 4, free, in two subequal whorls, 10–25 mm long × 3–5 mm wide, linear lanceolate to linear-triangular, whitish or beige, rarely yellowish green when immature, sparsely to densely pubescent outside, glabrous inside, acute at apex, base truncate and cusped around the stamens; outer petals, more or less thin, with faint venation, reflexed at anthesis; inner petals thicker, ~ 1 mm, and fleshier and not reflexed with a shallow, more or less triangular white patch near the base inside. Stamens, 40–45, 1–1.5 mm long, extrorse, filament very short, apical part of connective expanded over the thecae, shield-shaped, ellipsoid to angulate, glabrous. Carpels, 2–3 per flower, to 2 mm long; stigma more or less globose, to 0.5 mm diam., and essentially glabrous; style absent; ovaries ellipsoid and more or less curved, like a small banana with densely light-brown hairs; ovules 10–13, lateral, in two rows. Monocarps, 1-3 per fruit (frequently 2), large and fleshy, 5–7 cm long × 3–4 cm wide, ellipsoid, apex and base rounded, glabrous, shortly stipitate, stipes to 1 mm long or absent; young monocarps green, yellow to light brown when ripe with a peach-like sweet odor; seeds lunate to wedge-shaped, 1.7–2 cm long with lamellate ruminations.

Habitat and ecology:—The type locality of Tridimeris huatuscoana is located within one of the most important regions for coffee cultivation in Mexico, which is mostly covered by montane cloud forest. Interestingly, Tridimeris huatuscoana forms part of the riverine vegetation on limestone karst soils, along with Platanus mexicana Moricand (1837: 39) , Cojoba arborea ( L.) Britton & Rose (1928:29), Oreopanax xalapensis (Kunth) Decaisne & Planchon (1854:108) , Siparuna thecaphora (Poepp. & Endl.) Candolle (1868: 657) , Ardisia compressa Kunth (in Humboldt et al.1819: 245), Bunchosia biocellata Schlechtendal (1836: 241) , Trichilia martiana de Candolle (1878: 205) , Spathacanthus magdalenae Castillo-Campos (in Castillo-Campos et al. 2013: 449), Cnidoscolus multilobus (Pax) Johnston (1923: 86) , and Cornutia pyramidata Linnaeus (1753: 628) , as well as with some representative elements of the forest edge zones, such as Moussonia deppeana (Schltdl. & Cham.) Hanstein (1865: 284) . Individuals of Tridimeris huatuscoana are always present on the banks of the river, are scattered distributed, separated from each other by a few tens of meters.

The flowers of Tridimeris huatuscoana form a pollination chamber during anthesis, which is when the internal petals get closer to each other in such a way that the reproductive organs of the flower are covered ( Fig. 2E ). In this way, floral visitors are filtered so that only those that meet a certain body size could have contact with the carpels, thus carrying out pollination. In addition, the flowers have a white triangular patch at the base of the inner petals ( Fig. 1C ), a structure that signals a greater thickening of the petals and considered a reward for pollinators (food bodies, sensu Schatz et al. 2018). We did not observe floral visitors on T. hustuscoana but daytime pollination chamber observations might suggest that pollination of this species is diurnal.

Phenology:—The species has two flowering peaks, at the end of the year between October and December, where fruits can also be observed, and then at the beginning of the year between March and May, where fruiting is rather absent.

Seed germination:—We collected nine seeds of the new species and submerged them for 24 hours in water followed by sowing in bags with local enriched soil (30% black soil, 30% vermicompost, 20% tepezil and 20% coffee and sheep pulp fertilizer). The bags were kept constantly humidified (40%) for three months. Shortly after this (three months and two weeks) all seeds germinated and after six months they reach sizes of up to 10 cm ( Fig. 2H ).

Etymology:—The specific epithet is in honor of the municipality of Huatusco, in Veracruz, Mexico, one of the most important regions for coffee production, full of history and culture, and an obligatory path for many botanical explorers.

Conservation status:— Tridimeris huatuscoana is known only from the type locality in Huatusco, Veracruz ( Fig. 3 ). According to the criteria established by the IUCN, it is possible to tentatively determine that the species is Critically Endangered [CR B1ab (iii)]. The Area of occupancy (AOO) of T. huatuscoana is 4.0 km² and the Extent of occurrence (EOO) is 0.0 km², suggesting a very restricted overall distribution. Although the only known population of the species is located within a large fragment of montane cloud forest ( Fig. 4 ), the species appears restricted to the banks of a river where it is really scarce (less than 10 individuals in one hectare). In addition, the forests around the type locality are threatened by non-sustainable activities (logging, fires, illegal settlements and land use change) and at more local scales the forest is evidently fragmented characterized by many small isolated patches which are surrounded by roads, croplands and cattle pastures ( Fig. 4 ).

Additional specimens examined:— MEXICO. Veracruz: From the type locality, 4 September 2021, E. J .

Marinero-Sobal 426, 427,428 (MEXU).

Figures

FIGURE 1. Tridimeris huatuscoana. A) Habit. B) Branchlet with inflorescences. C) Dimerous flower, note the white triangular patch at base of inner petals (food bodies). D) Monocarps. (Photographs by Esteban Marinero-Sobal).

FIGURE 2. Tridimeris huatuscoana. E) Branchlet with inflorescences, note the color of the flowers and the pollination chamber. F) Setose pocket domatia. G) Close-up of the flower, note the two carpels surrounded by numerous stamens. H) Small plant of Tridimeris huatuscoana. (Photographs by Esteban Marinero-Sobal).

FIGURE 3. Distribution range of Tridimeris huatuscoana (black star), Tridimeris hahniana (blue squares) and Tridimeris chiapensis (purple dots). To the right and from top to bottom, flowers of Tridimeris hahniana, Tridimeris huatuscoana, and Tridimeris chiapensis.

FIGURE 4. The type locality of Tridimeris huatuscoana. The red box represents the Area of occupancy (AOO) accordingly to its conservation status assessment using the GeoCAT tool.