Reproductive Ecology of Maxillaria carinulata and Maxillaria meridensis (Orchidaceae) in the Andes of Caquetá, Colombia: Breeding System, Floral Visitors, Floral Compounds, and Pollen Transfer

Maxillariinae is one of the most diverse Neotropical orchid groups, yet little is known about its reproduction and pollination. We studied Maxillaria carinulata and Maxillaria meridensis on the eastern slope of the Cordillera Oriental in Caquetá, Colombia (2000–2300 m), using pollinator exclusion, controlled pollination, observations, and histochemical tests. Hand pollination was used for manual autogamy, geitonogamy, and xenogamy treatments. Bagged flowers produced no fruit, confirming dependence on pollinators. Apomixis and spontaneous selfing failed, but manual autogamy, geitonogamy, and xenogamy yielded high fruit sets, showing self-compatibility and cross-fertility. In M. carinulata, fruit set reached 93.3%, 86.7%, and 90%; in M. meridensis, 80.0%, 83.3%, and 86.7%. The independent natural fruit-set survey showed low fruit production under field conditions, with 4.7% of monitored flowers forming fruits in M. carinulata and 16.3% in M. meridensis, reflecting inefficient pollen transfer. Both species showed floral scent and osmophore-like activity; M. meridensis also produced lipids, proteins, sugars, and starch in specific tissues. Visitors, mainly Stethobaris weevils, were recorded on M. meridensis, but no pollinarium removal or deposition occurred. These findings highlight strong pollination limitations and support conserving habitats to sustain effective pollinators in Andean populations.