Floral morphology and pollen viability of an endangered and endemic Bromeliaceae species from the Atlantic Forest

The present study describes the floral morphology and evaluates pollen viability for the bromeliad Nidularium minutum Mez. during the flowering period 2018-2019 through histochemistry and pollen germination tests. The inflorescences are nidular, capituliform with short branches bearing two to three odourless, bisexual and greenish-white flowers and with an androecium shorter than the gynoecium, consisting of six stamens with anthers featuring rimose dehiscence. The ovules are anatropous, displaying a small appendage in the chalazal region. The first flower opened in late November 2018 and flowering peak was in January 2019. Anthesis started at 6:55 a.m. and lasted until 8:49 a.m. Pollen/ovule ratio indicates facultative autogamy. The pollen grains are monads, medium to large, 2-(3)-porate, reticulate heterobrochate with abundant pollenkitt. A high frequency of unviable pollen grains with discrepant sizes was observed. The mature pollen grain is considered recalcitrant and therefore sensitive to desiccation. In vitro pollen germination after 48 hours was higher in BKM medium (64.77%) compared to SM (38.51%). Pollen viability was overestimated in all histochemistry tests, with Alexander (72.46%) being the closest to the in vitro germination rate. The results obtained for N. minutum bring new information about its floral biology as a subsidy to the cultivation of ornamental bromeliads that are at risk of extinction.