Gonolobus glaberrimus (Woodson) Stevens (2005: 603)

Carnevali, Germán, Romero-González, Gustavo A., Tapia-Muñoz, José Luis, Ramírez-Morillo, Ivón M., Ramírez-Díaz, Claudia J., Cetzal-Ix, William, Stefano, Rodrigo Duno De & Romero-Soler, Katya J., 2022, Twice lost, twice found: A new species of Gonolobus (Apocynaceae: Asclepiadoideae) with a reappraisal of the genus in the Yucatan Peninsula Biotic Province, Phytotaxa 530 (2), pp. 141-162 : 155-156

Gonolobus glaberrimus (Woodson) Stevens (2005: 603)

≡ Matelea glaberrima Woodson (1941: 281) ≡ Atrostemma glaberrimum (Woodson) Morillo (2016: 91).

Type: — GUATEMALA, H. Bartlett 12300 (Holotype, MO /BC: MO-078253 /A:1041429, photo! ( Fig. 2D ); isotypes, MICH-1111617 , photo!, MO-1041473 ( Fig. 2C ), photo!, US-00111087 , photo!) .

= Matelea tikalana Lundell (1968a: 446) ≡ Marsdenia tikalana (Lundell) Lundell (1968b: 49) . Type: Guatemala: Dept. Petén: Tikal National Park, Tikal, “in ramonal bordering hotel, March 20, 1959 ”, C.L. Lundell 15763 (Holotype LL-00372545, photo!, isotype, MO-344433, photo!).

Notes:—A distinctive species whose generic position has been long disputed. The glabrous, lanceolate foliar blades, at least three times longer than wide are unusual in Gonolobus and unique in the YPBP among members of the genus. The foliar blades are only shallowly cordate at the base; all other Gonolobus in the area have predominantly ovate, ovateelliptic, or ovate-oblong foliar blades that are sharply cordate at base and only about 2–2.5 times longer than wide. The flowers of this species are relatively small with white corolla lobes 7–8 × 3.5–4 mm. This species is closely related to the extralimital G. hammelii W.D. Stevens (2005b: 235) (from Costa Rica), G. hadrostemma Stevens (2005b: 233-235) ( Nicaragua and Costa Rica), Matelea manarae Morillo (in Steyermark 1978: 48-49) (from coastal Venezuela) and a few others. All feature similar foliage and are atypical in Gonolobus in having a massive corona adnate to the faucal annulus. Furthermore, the anthers lack the free appendages that characterize the genus ( Stevens 2005b). These species have been transferred to Atrostemma Morillo (2015b: 198) , a taxonomic decision that may have some merit.

Gonolobus glaberrimus is known from two collections, both from the Guatemalan Petén, where it grows in tropical rain forest at elevations of 175–190 m. It is probably a rare, inconspicuous species and probably difficult to spot even in flower or fruits. There is a collection at MO (I Inbio 159, photo!) from Estación Biológica Maritza, Guanacaste, Costa Rica identified as this species by a specialist (J.F. Morales). However, the specimen is poor, the leaves are all folded-up and the shape looks somewhat different.Also, it does not have mature flowers (“immature fruits”), which are necessary for positive identification. Furthermore, it is isolated from the other three localities by more than 850 km. Because of all these arguments, we have decided to consider G. glaberrimus as endemic to the southern portion of the YPBP until more conclusive evidence proves otherwise ( Figs. 1C , 2 C-D) .

IUCN Conservation assessment.—EN. Gonolobus glaberrimus is known from only two localities and three collections. Thus, AOE cannot be estimated at this time and the AOO is of 8 km 2. The two localities are 18–19 km apart. It is likely that the species is restricted to the area of the Guatemalan Petén and that when further localities are recorded, we will be able to reassess its conservation status probably as EN (Endangered). Although the species is rare, its known populations are located the Tikal National Park, which affords them some degree of protection for the foreseeable future.

Specimens examined: — GUATEMALA. Petén: Tikal National Park, on [along] Remate Road , 17°13’30” N, 89°36’47” W, 190 m, 15 January 1962, C.L. Lundell 17103 ( LL, MO) .

Figures

FIGURE 1. Distribution of Gonolobus species in the Yucatan Peninsula Biotic Province (YPBP). A. Southern Megamexico, including the YPBP, and Central America. The green line is the border of the YPBP. B. Distribution of Gonolobus barbatus, G. caamalii, and G. cteniophorus. C. Distribution of G. fraternus, G. glaberrimus, and G. leianthus. D. Distribution of G. stenanthus and its subspecies.Empty circles with a black dot inside represent collections that we have been unable to refer unambiguously to subspecies because specimens are sterile or fruiting. Maps drawn and edited by Claudia J. Ramírez and William Cetzal-Ix.

FIGURE 2. Gonolobus barbatus and G. glaberrimus. A. Gonolobus barbatus. Original plate in the protologue of the species (Kunth in Humb., Bonpl.Kunth, Nov. Gen. Sp. (quarto e.) 3: t. 239 (1819). B. G. barbatus, Lectotype, Humboldt & Bonpland s.n. (P-P00670906).C- D. G. glaberrimus, type collection, C. MO-078253 isotype (downloaded from http://legacy.tropicos.org/Image/27408), D. US-00111087, isotype (downloaded from https://ids.si.edu/ids/media_view?id=ark:/65665/m3b941b8915300447c9420f9259ef2d963&defaultView=im age_dynamic).