Comparative anatomy and morphology of the fleshy fruit and the first record of seedlings in Olmeca reflexa in Bambusoideae (Poaceae)

- Mature fruits of O. reflexa have a vestigial endosperm.
- Vestigial endosperm is shared with other woody bamboo genera.
- O. reflexa has a well-developed pericarp and scutellum.
- Fleshy fruits favor fast germination and seedling grow.

Although the great majority of the genera in Poaceae possess the characteristic caryopsis fruit, a number of species in twelve genera in different clades in subfamily Bambusoideae have evolved bacoid or fleshy fruit. In this paper we describe the anatomy and morphology of the fleshy fruit of the Neotropical woody bamboo Olmeca reflexa and include remarks on its seedlings. We compare its main anatomical and morphological characters with other genera in Bambusoideae with this specialized type of caryopsis. Mature fruits in Olmeca reflexa are globose, and they vary from 2 to 4 cm diameter; the pericarp surface is smooth and its texture is hard. In immature fruits, the endosperm occupies the central cavity in the form of mucilaginous ivory-white tissue, whereas in mature fruits the endosperm is vestigial. In the embryo, the scutellum is well developed, the plumule and radicle are basal, the embryo has a coleoptile enclosing the embryonic leaves, the coleorhiza and lower part of the scutellum are separated by a distinct cleft, and it does not have an epiblast. Fruits show similarities with the species of eleven other fleshy-fruited genera in Bambusoideae. Vestigial endosperm in mature fruits is found in species of Cyrtochloa, Dinochloa, Melocanna, Melocalamus, Ochlandra, Olmeca recta and Sphaerobambos but it is well developed in Alvimia, Guadua sarcocarpa and Stapletonia. Fleshy fruits in woody bamboos are highly specialized and a number of hypotheses have been proposed on their function, such as providing water and nutrients for fast germination and vigorous seedling growth.

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