Mendoncia amabilis F.A.Silva, 2023

Silva, Fabio Araújo Da, Kameyama, Cíntia, Betancur, Julio & Zappi, Daniela C., 2023, Mendoncia amabilis (Acanthaceae), a remarkable new species from the Amazon basin, Phytotaxa 612 (2), pp. 229-236 : 230-235

Mendoncia amabilis F.A.Silva sp. nov. ( Figs.1–2 )

Type:— COLOMBIA. Departamento Amazonas: Corregimiento La Pedrera , resguardo indígena Curare—Los Ingleses , comunidad Curare , 1º 17’ S 69º 44’ W, 100 m, rebalse del río Caquetá, 1 km arriba de la desembocadura del quebradón Curare, 10 March 2004, fl., Z. Cordero-P., A. Cubeo & R. Miraña 407 (holotype: COL000373340 !; isotype: MG!) .

Diagnosis:— Mendoncia amabilis resembles M. squamuligera Nees (1847: 50) and M. tonduzii Turrill (1919: 413) in the subquadrangular branches, membranous leaves, canaliculate petioles, predominantly white, infundibuliform and ventricose corolla, but differs by having strigose petiole (vs. densely pubescent), leaf-blade sparsely strigose to glabrescent beneath (vs. densely pubescent), broad membranous bracteoles 2.8–3.8 × 1.5–1.7 cm (vs. subcoriaceous, 3.5–4 × 1–1.3 cm in M. squamuligera and membranous, 3–3.8 × 1–1.3 cm in M. tonduzii ), calyx hirsute (vs. glabrous in M. squamuligera and puberulous in M. tonduzii ), and ovary sericeous (vs. glandular-papillose in M. squamuligera and puberulous in M. tonduzii ).

Description:—Twining vine. Branches subquadrangular, sulcate, golden pubescent when young, eglandular trichomes, appressed, internodes 6–17 cm long. Leaves membranous; petiole 1.2–2 cm long, canaliculate, strigose; blades 8.5–11 × 4.8–6 cm, oblong to elliptic, sparsely strigose to glabrescent with eglandular trichomes with type 3 basal cells on both sides, base rounded to obtuse, margin entire, apex acuminate, with mucron 2–2.5 mm long, venation camptodromous, secondary veins 3–4 pairs, median and secondary veins prominulous above, prominent beneath. Flowers 1–3 clustered in the leaf axils; pedicels 2.2–3.3 cm long, strigose; bracteoles 2.8–3.8 × 1.5–1.7 cm, green, oblong, fused up to the middle, membranous, base rounded to truncate, apex cuspidate, mucron 1–1.2 mm long, midrib slightly prominent, external surface golden-pubescent, denser at margins, eglandular trichomes with type 1 basal cells, 0.8–1 mm long, internally papillose-glandular; calyx 1.8–2 × 3.2–3.5 mm, margin entire, hirsute, with erect eglandular and glandular trichomes; corolla 4.5–5.8 cm long, white, with purple nectar-guides at the throat, infundibuliform, ventricose, glabrous externally, glandular-papillose within, basal tube 0.6–0.7 cm wide, decreasing to 0.45–0.5 cm wide above the ovary region, throat 0.5–0.6 cm wide, mouth of the corolla 1–1.2 cm wide, upper lip two-lobed, strongly reflexed, lower lip three-parted, spreading, lobes 0.7–0.8 × 0.6–0.7 cm, orbicular, apex retuse; stamens 4, fused to the middle of the corolla-tube, free portion of the filaments 2–4 mm long; thecae with a basal tuft of eglandular, bristly trichomes, connective with sparsely glandular trichomes, anthers sagittate, dorsal pair 0.8–1 cm long, ventral pair 0.9–1 cm long; pollen grains 5-brevicolpate, rugulate over the interapertural surface; ovary 2.8–3 × 2.8–3 mm, sericeous; style 3.7–4.8 cm long, proximally hirsute with sparse glandular trichomes, distally glabrous, stigma bilobed, lobes subequal, ca. 0.1 mm long. Drupe (immature) 1.4–1.6 × 0.7–0.9 cm, ellipsoid, pubescent, with erect eglandular trichomes.

Distribution and Habitat:— Mendoncia amabilis is a northwestern Amazon basin taxon known only from three localities in Colombia and a single locality in Peru ( Fig. 3 ), occurring at river margins or close to river banks, at altitudes below 100 m.

Preliminary Conservation Status:—With only four known sub-populations, the extent of occurrence of Mendoncia amabilis is 155,993.361 km 2 while the area of occupation is 16 km 2. Despite of its small area of occupation, there is no evidence of discontinuity of the subpopulations and no threats have been recorded so far in such remote areas of Colombia and Peru. Therefore, we consider it Data Deficient (DD), since new collections are needed to improve our knowledge regarding the conservation status of this new species.

Phenology:—The species was collected flowering in March and April and fruiting in April.

Etymology:—The specific epithet ‘ amabilis ’, meaning lovely, refers not only to the beauty of the plant with showy corollas, but also to the extremely friendly and amiable reception the first author experienced when visiting the Colombian herbaria in 2022.

Additional specimens examined (paratypes):— COLOMBIA. Departamento Amazonas: Corregimiento Tarapacá, resguardo indígena ASOAINTAM, caño Sucuruyu, márgenes derecha e izquierda subiendo a C001213 del IFN, 2°58’ S 69º50’ W, 67 m, 16 April 2019, fl., M. Rodríguez et al. 4026 ( COAH!) . Departamento Caquetá: Orilla izquierda del río caguán, 16 horas en motor Johnson de 10 H. P. al sur de Cartagena , 24 April 1953, fl., R. Romero-Castañeda 4086 ( COL!, MO!) . PERU. Departamento Loreto: Maynas, Dtto. Sargento Lores , río Amazonas, Isla de Aguajal , 90–95 m, 9 March 1982, fl., S. McDaniel & M. Rimachi Y. 25722 (AMAZ!) .

Discussion:—In the Catalogue of plants from Colombia, 37 species of Mendoncia were recorded from Colombia, among which 16 are endemic ( Wood 2015). This genus has its highest number of species in that country, with between 35 and 40 species recorded ( Magnaghi & Daniel 2017). Extensive searches among type-collections from Northwestern South America were carried out to ascertain that this taxon had not been previously described.

Mendoncia amabilis is characterized by its showy large oblong bracteoles, and white corolla, its golden-pubescent branches, strigose petiole and pedicels, and both surfaces of the leaf-blade clad with eglandular trichomes with type 3 basal cells ( Fig. 4A–B ) on both sides ( Silva et al. 2023). This new species keyed out near M. coccinea Vellozo (1829: 263) [= M. velloziana Martius (1829: 22) ] in the identification key provided by Leonard (1951) and updated by Wasshausen (1989). This was due to its pubescent branches, appressed trichomes and wide pubescent bracts with rounded base. However, the new species is easily distinguished from M. velloziana due to its subquadrangular branches (vs. subcylindrical), strigose petiole and pedicel (vs. densely pubescent), 2.8–3.8 cm long bracteoles (vs. 2–2.5 cm long), corolla mostly white with purple nectar guides at the throat (vs. evenly red) and hirsute calyx (vs. glabrous).

From our ongoing studies, the new species is most similar to Mendoncia squamuligera and M. tonduzii in their subquadrangular branches, membranous leaf-blades, and white corolla with purple nectar guides, however it differs in bracteole characters, which are membranous, 2.8–3.8 × 1.5–1.7 cm, vs. subcoriaceous, 3.5–4 × 1–1.3 cm in M. squamuligera , and membranous, 3–3.8 × 1–1.3 cm in M. tonduzii ( Fig. 5 ). Moreover, the bracteoles are only fused up to the middle in M. amabilis while fused up to the upper third in M. squamuligera and M. tonduzii . Flower details of these species are also different, M. amabilis has hirsute calyx and sericeous ovary ( Fig. 1G ), while in M. squamuligera the calyx is glabrous, and the ovary is glandular-papillose; whereas, the ovary and calyx are puberulous in M. tonduzii . Another difference is that the style of M. amabilis is proximally hirsute and distally glabrous, whereas in M. squamuligera the style is totally glabrous and in M. tonduzii the style is proximally glandular and distally glabrous ( Table 1 ). The palynological study revealed typical spheroidal Mendoncia 5-aperturated pollen grains poorly ornamented, finely rugulate exine in the interapertural surfaces, as found by Magnaghi & Daniel (2017) in African species of the genus ( Fig. 2 D–F ).

Considering that one of the collections of this new species remained unnamed and undescribed for more than 60 years suggests that the Amazonian flora is still in need of in depth field and collection studies, as already pointed out by several researchers ( Barbosa-Silva et al. 2021, Brazil Flora Group [BFG] 2015, Cardoso et al. 2017).

Figures

FIGURE 1. Mendoncia amabilis. A. Flowering branch. B. Adaxial surface of the leaf. C. Adaxial surface of the bracteole. D. Stamens inside of the corolla. E. Anther. F. Bracteole and gynoecium. G. Ovary and calyx. H. Detail of the stigma. Drawn by Carlos Alvarez based on Z. Cordero-P. et al. 407 (COL!).

FIGURE 2. Mendoncia amabilis. A. Flowering branch. B. Anther. C. Hairs at the base of the anthers. D. Pollen, polar view. E. Ornamentation of the exine. F. Pollen colpi, equatorial view. A. Photo by A. Baraona. B–F from Z. Cordero-P. et al. 407 (COL!).

FIGURE 3. Distribution map of Mendoncia amabilis.

FIGURE 4. SEM of leaf blade and bracteole of Mendoncia amabilis and similar species.A–B. M. amabilis. A. Leaf-blade. B. Bracteole. C–D. M. squamuligera. C. Leaf-blade. D. Bracteole. E–F. M. tonduzii. E. Leaf-blade. F. Bracteole. A–B. from Z. Cordero-P. et al. 407 (COL!). C.D. J.T.F. Guimarães et al. 34 (MG!). E–F. L. Castaño-Rosalba & G.E. Muñoz 148 (HUA!).

FIGURE 5. Bracteole morphology of Mendoncia amabilis and similar species. A. M. amabilis. B. M. squamuligera. C. M. tonduzii. A. from Z. Cordero-P. et al. 407 (COL!). B. J.T.F. Guimarães et al. 34 (MG!). C. L. Castaño-Rosalba & G.E. Muñoz 148 (HUA!).