Gonolobus leianthus Donnell Smith (1909: 296)

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 : 156-158

Gonolobus leianthus Donnell Smith (1909: 296) .

Type: — GUATEMALA. Dept. Alta Verapaz, Cubilquitz , 350 m, October 1901, H. von Türckheim 8243 (Holotype, US-01338610 , photo!) .

= Vincetoxicum schippii Standley (1930: 37) . Type : British Honduras, Middlesex, in open places, alt. 60 m, 15 September 1929, W.A. Schipp S-19 (Holotype, F-602928, photo!; isotype GH-00076892 , photo!).

Notes:—This species has green, almost featureless flowers. The calyx lobes are broadly triangular, patent and conspicuous in both live and herbarium material. The corolla lobes are relatively large and conspicuous, 18–34 × 6–12 mm, asymmetrically elliptic, acuminate. They have a white callus along one of the margins and there is a conspicuous, narrow white ring around the gynostegium. Gonolobus leianthus is relatively widespread in the southern portion of Megamexico from Tabasco and Chiapas to northern Nicaragua. It occurs in tropical humid or cloud forests at elevations of 60–1400 m ( Figs. 1C , 3D ).

Specimens examined: — GUATEMALA. Petén: Dolores, between km 73/72 of Santo Toribio road, 16°31’45” N, 89°27’15” W, 21 July 1961, E. Contreras 2637 ( CAS, MEXU, MO, TEX) ; Dolores, bordering Río Ixcol , 1 km East, 16°30’45” N, 89°23’54” W, 3 June 1961, E. Contreras 2415 ( TEX) ; La Cumbre, km 138/137 of Cadenas Road , 16°04’52” N, 89°21’03” W, 270 m, 26 September 1966, E. Contreras 6246 (F, LL, MEXU, MO) ; La Cumbre, bordering Cadenas Road , km 143, 16°04’52” N, 89°21’03” W, 270 m, 1 September 1969, E. Contreras 9036 ( CAS, DUKE, MO, TEX) ; San Luis , 16°11’59” N, 89°26’31” W, 12 July 1959, C.L. Lundell 16385 ( CAS, F, MO, TEX) ; Tikal, Tikal National Park , 17°13’30” N, 89°36’47” W, 4 July 1959, C.L. Lundell 16172 ( CAS, DUKE, F, MEXU, MO, TEX) ; 24 September 1959, E. Contreras 168 ( CAS, F, MO, TEX) ; Tikal, Parque Nacional, frente Templo No. 4, 17°13’30” N, 89°36’47” W, 8 November 1969, R. Tun Ortíz 428 ( DS, F, MO) .

Gonolobus stenanthus (Standley) Woodson (1941: 243) ≡ Vincetoxicum stenanthum Standley (1929: 255) ≡ Matelea stenantha (Standley) Shinners (1964: 366) .

Type: — BELIZE. Tower Hill, 1928, J. S. Karling 27 (Holotype, F-0044022F, photo!; isotype US-00112339 , photo!) .

Notes:— Gonolobus stenanthus is one of the endemic species of the YPBP. It is readily diagnosed by its relatively large, conspicuously reflexed calyx lobes (11–14 × 3.8–5.5 mm), which are easily visible both in live and in herbarium material. Furthermore, the corolla lobes are triangular-lanceolate, acute, and the right margin is bright white. The corona is bright yellow, pubescent. This species is relatively widespread within the YPBP, particularly in the eastern and southern portions, covered by seasonally dry forests with precipitations in the range of 1000–1500 mm.

Recent treatments of the Gonolobus of the YPBP ( Stevens 2010; Carnevali et al. 2010) have treated G. yucatanensis as a synonym of G. stenanthus . Both entities are vegetatively indistinguishable and dry flowers look extremely alike. However, G. stenanthus comes in two color morphs. In the type collection (J.S. Karling 27, F, photograph!, type of the basionym, Vincetoxicum stenanthum Standley (1929: 255) , the flowers have dried of a dull pale green, a pattern associated with the typical green corollas of the species in populations coming from northern Belize, the Guatemalan Petén, and southern Quintana Roo and Campeche. Thus, plants matching this type have bright green or yellow-green petals; the stylar head of the gynostegium as well as the anther appendages are yellow ( Fig. 1D , 3 E-F). However, populations of G. stenanthus on the northern, drier edge of its distribution in eastern Yucatán and northern Quintana Roo States, typically feature extremely dark chestnut to reddish brown, almost black corollas ( Fig. 1D , 3 G-I). The type of Trichostelma yucatanensis (Steere 2641, MO) is very poorly preserved, but the original diagnosis clearly states that the flowers have an “… atrocarneae …” corolla, which indicates that the name can be applied to the dark-colored populations on the northern edge of the distribution of G. stenanthus . Furthermore, while the corona is also bright yellow (as in typical plants), the stylar head of the gynostegium and the anther appendages are dark reddish maroon, creating a sharp color contrast. Photographs of both color morphs of the species are strikingly distinct, suggesting they may be reproductively isolated and could constitute different species.

Because the dark colored populations are geographically restricted but contiguous to the typical, more common and more southernly distributed green-flowered populations, and both sets of populations are morphologically distinctive in flower color and ecologically different, we propose to treat Gonolobus yucatanensis as a subspecies of G. stenanthus .

This decision requires the following nomenclatural change:

Gonolobus stenanthus subsp. yucatanensis (Woodson) Carnevali & R.Duno , comb. nov. ≡ Trichostelma yucatanense Woodson (1935: 691) ≡ Gonolobus yucatanensis (Woodson) Stevens (1983: 405) .

Type: — Mexico: Quintana Roo: in low forest, San Miguel, Cozumel Island , 6-8 Aug 1932, W.C. Steere 2641 (Holotype, MO /BC: MO-078214 /A:1064813, photo!; isotypes MICH- 1000055A, photo!, MICH- 1000055B, photo!).

IUCN Conservation assessment: Here we will assess the species a as a whole and the subspecies individually.

Gonolobus stenanthus —NT. The species meets criterion B1 a, b (i, ii, iii, iv) for a Least Concern species ( LC) and B2 a, b (i, ii, iii, iv) for Endangered species ( EN). It is known to us from 27 localities in the three Mexican states of the YPBP, as well as from northern Belize (Orange Walk). Its extent of occurrence is of 77,475.415 km 2 ( LC) and its AOO= 96.000 km 2 ( EN). Furthermore, the species does not have two of the three additional conditions to meet the requirements for neither the category of an Endangered ( EN) nor a Vulnerable (V) species. For this reason, as well as the occurrence of the subspecies in two naturally protected areas (Calakmul Biosphere Reserve, and Sian Ka’an Biosphere Reserve), we propose the species to be treated as Near Threatened ( NT).

Gonolobus stenanthus subsp. stenanthus —NT. Occupying most of the range of the species, this subspecies is the most common and widespread with 20 collection localities, with an EOO= 59,039.2 km 2 ( LC) and an AOO=72.0 km 2 ( EN). All the statements for the whole species apply here.

Gonolobus stenanthus subsp. yucatanensis —EN. This subspecies is currently known from seven localities and has an EOO of 3,565.9 km 2 ( EN) and an AOO of 28.0 km 2 ( EN). Most of the localities for this species are in areas where anthropic disturbances are strong and are likely to become subject to increased pressure. Several of the known localities are in the vicinities of large urban centers (Valladolid in Yucatán, Tulum in Quintana Roo) and will be most likely soon affected. However, the species has been collected near at least three protected archaeological zones (Chichén Itza, Coba, and Tulum) where at least some degree of protection for the foreseeable future is guaranteed.

Specimens examined:— Gonolobus stenanthus subsp. stenanthus . MEXICO. Campeche: Mun. Calakmul, Zoh-Laguna , 18°35’39” N, 89°24’48” W, 290 m, 19 May 1997, P. Álvaro M. & D. Álvarez 730 ( MEXU); a 2 km al W de Calakmul, camino a La Laguna , 18° 7’28” N, 89°48’56” W, 184 m, 12 July 1997, E. Martínez S., D. Álvarez & S. Ramírez 27689 ( MEXU) ; Ejido Nuevo Becal , parcela 6, 18°40’54” N, 89°23’47” W, 16 August 2006, M.A. Islas Luna 1950 ( CICY, CIQR) ; Cerro Civalito, km 4.5 carretera Civalito-Dos Lagunas , 17°52’43.5” N, 89°20’29.1” W, 200 m, 8 July 2009, L. Ibarra & A. Torres C. 603 ( CICY) ; 22 July 2009, L. Ibarra & A. Torres C. 609 ( CICY) ; Mun. [Calakmul], 6 km al O de la desviación a Calakmul, aprox. km 105 de la carr. Escárcega-Chetumal , approx. 18°32’35” N, 89°57’24” W, approx. 159 m, 30 July 1987, E. Cabrera & H. de Cabrera 14176 ( MEXU) ; 12 km al S de Conhuas, sobre el camino al centro Ceremonial de Calakmul, entrando por el km 98 de la carretera Escárcega-Chetumal , 18°28’ 2” N, 89°53’30” W, 27 July 1986, E. Cabrera C. & H. de Cabrera 11845 ( MEXU) ; Mun. [Carmen], Monterrey , approx. 18°23’60” N, 91° 7’ W, 23 January 1932, C.L. Lundell 1237 ( DS, F, MO, NY, WIS) ; Mun. Hopelchén , a 2.44 km al NO de Pachuitz, 19°9’53” N, 89°15’24” W, 143 m, 29 May 2004, D. Álvarez 8823 ( MEXU) ; a 2.3 km al S de Chan-Chen, camino a Pachuitz , 19°11’15” N, 89°15’42” W, 136 m, 16 June 2004, D. Álvarez, A. Ramírez, C.H. Ramos, E. Martínez S. & F. Sosa M. 9230 ( MEXU) ; a 3.2 km al SE de Chan-Chen , 19°11’18” N, 89°14’26” W, 113 m, 13 June 2004, D. Álvarez, A. Ramírez, C.H. Ramos, E. Martínez S. & F. Sosa M. 9032 ( MEXU) . Quintana Roo: Mun. Benito Juárez, a 1 km al Este de la Cd. Cancún , approx. 21°19’50” N, 86°48’30” W, 12 September 1982, E. Cabrera & H. de Cabrera 3482 ( MEXU) ; Mun. F. Carrillo Puerto, a 44 km al Norte de F. Carrillo Puerto , approx. 19°55’30” N, 88°12’34” W, 9 September 1980, O. Téllez, E. Cabrera & L. Rico 3509 ( MEXU) ; 10 km al NE de F. Carrillo Puerto sobre el camino a Vigía Chico , approx. 19°37’15” N, 87°57’30” W, 6 July 1989, E. Cabrera 16475 ( MEXU) ; Mun. [Tulum], Cobá , zona arqueológica, sacbé # 1 y # 3, 20°30’40” N, 87°43’10” W, A. Barrera 484 ( CICY) ; Cobá, zona arqueológica, grupo Cobá , 20°29’15” N, 87°44’ W, 15 May 1981, E. Ucán & J.S. Flores 1120 ( CICY) ; 22 March 1994, R.R. Sears 75 ( CICY) . Yucatán: Mun. Tekax , a 18.9 km al ESE de Nohanal, 19°43’45” N, 89° 9’58” W, 90 m, 17 June 2004, D. Álvarez, A. Ramírez, C.H. Ramos, E. Martínez S. & F. Sosa M. 9293 ( MEXU) . BELIZE. Orange Walk: Vicinity of Tower Hill , 18°01’ N, 88°31’ W, 1928, J.S. Karling 27 (F, MO) ; Honey Camp , 18°02’ N, 88°26’ W, October 1929, C.L. Lundell 536 ( DS, F) .

Gonolobus stenanthus subsp. yucatanensis . MEXICO. Quintana Roo: Mun. Cozumel, San Miguel in forest of Cozumel Island , 20°29’18” N, 86°55’56” W, 6–8 August 1932, W.C. Steere 2641 ( MICH, MO); Mun. [Tulum], Ruinas de Cobá , approx. 20°29’30” N, 87°43’55” W, 28 June 1986, J. Palma G. s.n. ( CIQR, MEXU) ; 20°31’ N, 87°39’ W, June-July 1938, C.L. Lundell & A.A. Lundell 7700 (A, F, GH, MICH, NY, SMU, TEX) ; 20°28’48” N, 87°43’48” W, June-July 1938, C.L. Lundell & A.A. Lundell 7765 ( MICH, TEX) ; C.L. Lundell & A.A. Lundell 7801 ( MICH) ; along road from Tulúm to Cobá , approx. 20°17’20” N, 87°30’15” W, 26 June 2002, P. Acevedo & F. May Pat 12190 ( CICY, NY, US) . Yucatán: Mun. Tinúm, Chichén Itza , near Pisté , approx. 20°40’15” N, 88°34’20” W, June-July 1938, C.L. Lundell & A.A. Lundell 7577 ( GH, MEXU, MICH) ; Mun. Valladolid, La Isla, un centro de descanso y gasolinera, km 143 autopista Mérida-Cancún , 20°44’39.62” N, 88°13’52.96” W, 27–30 m, 9 August 2018, G. Carnevali, R. Duno & J. Márquez 8377 ( CICY, CHIP, CIQR, F, FCME, G, GH, MEXU, MO, SEL, UADY, UCAM, UJAT, XAL) .

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 3. Gonolobus species of the YPBP.A. Gonolobus barbatus (based upon G. Carnevali 8584, CICY). B. G. cteniophorus (based upon G. Carnevali 7547, CICY). C. G. fraternus (based upon L. Ibarra-González s.n. (unvouchered)). D. Gonolobus leianthus (B.K. Holst s.n, SEL). E-F. Gonolobus stenanthus subsp. stenanthus (based upon L. Ibarra-González 603, CICY). G-I Gonolobus stenanthus subsp. yucatanensis (G based on Diana Beas s.n., unvouchered. H. based upon M.A. Caamal 01, CICY; I. (Based upon G. Carnevali et al. 8377, CICY, GH, MO). Photographs: A-B and I, G. Carnevali. C and E-F, León Ibarra González. D, Bruce K. Holst, downloaded from https:// www.naturalista.mx/observations/35867653) G, Diana Beas, downloaded from https://www.naturalista.mx/observations/54694745; H, Miguel Ángel Caamal.