New insights into anatomical and morphological adaptations to high elevations in the Melastomataceae: Evidence from Chaetolepis cufodontisii and Monochaetum amabile

• Adaptations to high elevations were documented in two Central American Melastomes.
• Likely adaptations to high elevations documented include amphistomy and a leaf hypodermis.
• An unusual finding were stomata in the anther walls of Chaetolepis cufodontisii.
• The particular type of herkogamy in Chaetolepis is established.
• Comparison to Andean taxa revealed more adaptations in the Central American species.

The anatomy and morphology of a representative each of the genera Chaetolepis and Monochaetum were studied from Costa Rica. Both species showed adaptations for inhabiting high elevations, especially Chaetolepis cufodontisii, which is the only representative of this mainly Andean genus in Central America and is restricted to the páramos of Costa Rica. The latter has amphistomatic, ericoid leaves with unusual glands on the adaxial leaf surface, stomatal crypts and glands in the abaxial surface, stomata on the anther walls, and a double lining of druses in the hypanthium. In the case of Monochaetum amabile, the leaves have a hypodermis and lack stomata on the adaxial leaf surface as well as conspicuous glands or stomatal crypts, and the hypanthium has a single, sparser lining of druses. A comparison between the leaves of each of the species in this study with species previously studied form South America shows that the Costa Rican representatives of each of these genera show more significant anatomical and morphological modifications for living at high elevation than their South American counterparts. A type of herkogamy that involves the style bent in opposite direction of the stamens is here confirmed in Chaetolepis cufodontisii. This type of herkogamy is shared with other species of Chaetholepis as well as its closest relatives that occur at the highest elevations in the Andes, Busquetia and Castratella. Some species in other more distantly related genera at elevations as low as sea level such as some Blakea also show this type of herkogamy suggesting this floral type is associated to pollinators regardless of the elevation the plants inhabit.

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