Pupulin, Karremans & Pupulin & Damián-Parizaca, 2025

4. Vanilla subgen. Tethyos Karremans , Damián & Pupulin , subgen. nov.

Type species:— Vanilla africana Lindley (1862: 137) View in CoL .

Etymology:— Tethyos is the genitive of Tethys , a word of Greek origin which means ancient sea or sea goddess. Tethys was the name of the prehistoric ocean located between the ancient continents of Gondwana and Laurasia, and bordered by the continents of Africa, Eurasia, India, and Australasia.

Diagnosis:—Nomadic or lithophytic vines, the leaves non-articulate, distichous, mostly with well-developed blades, but sometimes retaining deciduous scale-like leaves in several unrelated groups of species. Differing from the typical subgenus by the having flowers white or yellow, the lip typically notoriously stained with red, pink or purple (vs. lip similar in color to sepals and petals, not red, pink or purple), conical to saccate, the basal claw diversely fused to the column, typically forming a narrow, dry, papillose-hirsute, basal nectary, but not always forming an extended floral tube; the apical portion of the lip free, often flabellate, broadly expanding, with margins recurved. Sepals and petals often elliptic, broad (vs. lanceolate, narrow). Column shorter than the lip, with or without hairy ventral surface (vs. ventral surface hirsute), stigma a transverse cavity, the lateral lobes non-emergent (vs. emerging, flap-like). Pollen in monads, forming four easily disrupted masses. Fruits curved (vs. straight), non-calyculate (vs. calyculate), dehiscent (vs. either dehiscent or non-dehiscent), non-aromatic (vs. aromatic), specifically lacking vanillic and anisic compounds.

Discussion:— Vanilla subgen. Tethyos is the most diverse and broadly distributed subgenus of Vanilla . It currently includes 70 species across tropical Africa, Asia and the Antilles. They produce fleshy fruits, that are apparently dehiscent, and so-called non-aromatic. The fruits are actually not odorless, but none are known to contain compounds in the vanillyl, p-hydroxybenzyl and anisyl families, which give the fruits their characteristic vanilla-like smell and commercial interest.

As noted by Soto Arenas & Cribb (2010), Vanilla sect. Aphyllae as defined by Rolfe is polyphyletic. However, all species assigned by Rolfe to that section were placed by Soto Arenas & Cribb in their newly proposed V. sect. Tethya. This means that the lectotypification of V. sect. Aphyllae with any of its 12 species renders V. sect. Tethya illegitimate. Therefore, we selected the same type species as the two are unavoidably nomenclatural synonyms. Most species of Rolfe’s Vanilla sect. Aphyllae , typified by V. phalaenopsis , are endemic to the Indian Ocean basin, forming a distinct clade ( Fig. 1 View FIGURE 1 ) featuring leafless plants, showy white or yellowish flowers with maroon blotches on the lip, broad petals, and a loss of the penicillate callus. They seem to be closely related to a group of leafless New World species, which are endemic to the Antilles and differ in having narrow sepals and petals and a penicillate callus. These taxa, together with a few species from mainland Africa form our expanded circumscription of V. sect. Aphyllae , a section here including 22 species and being the only one in the genus that shows pantropical distribution. They are sister to a clade that is here given the new name V. sect. Miguelia , and which includes 37 exclusively Asian species, endemic to India, the Indo-China region and South-East Asia. Finally, both clades are sister to yet another Old World group, V. sect. Tethyos which includes 11 species exclusively known to occur in the tropics of Central and Western Africa.

Ecology:—Most members of Vanilla subgen. Tethyos seem to have sweetly fragrant flowers that appear to be dependent on pollinating bees to ensure reproduction (Watteyn et al. 2023), but observations on the pollination of flowers of species belonging to this subgenus are scanty. While the New World species are apparently pollinated by bees in the genus Centris (Centridini), their Old World relatives seem to be pollinated by bees in the genera Allodape (Allodapini) and Trinchostoma (Halictini).

Although morphologically similar to species of Vanilla subgen. Vanilla , the members of Vanilla subgen. Tethyos are neither pollinated, nor dispersed by the exclusively Neotropical Euglossine bees. Florally, many species belonging to both subgenera are similar in being mainly food-deceptive, having a dry, narrow nectary formed by the fusion of the claw of the lip and the base of the column. The column is elongate, and a penicillate callus in the middle of the lip blade is key in placing and removing the pollen masses as it forces the insect against the anther and stigma while it attempts to reach the basal nectary. The long-tongued Euglossini are needed in order to reach the nectary in Vanilla subgen. Vanilla , and it is therefore not surprising that some members of Vanilla subgen. Tethyos are pollinated by long-tongued counterparts in the Allodapini ( Gigant et al. 2014; 2016).