Background:

Acaciella (Mill.) Britton & Rose is a Neotropical genus, whose species were within the subgenus Aculeiferum (tribe Acacieae), due to morphological similarities. Molecular studies reflect a close phylogenetic relationship with the genus Calliandra (tribe Ingeae). At present, studies of floral development are lacking for Acaciella, which could provide morphological evidence related to the evolutionary history of both tribes.

Questions:

Will the floral development patterns of Acaciella angustissima be similar to those reported for species of Acacieae and Ingeae tribes?

Studied species:

Acaciella angustissima (Mill.) Britton & Rose

Study site and dates:

Pie de Vaca, Tepexi de Rodríguez, Puebla, Mexico, May 2014.

Methods:

Flower buds and mature inflorescences were collected and dissected for their observation with the scanning electron microscope.

Results:

Andromonoecious species with flowers in capitate inflorescences. The inflorescence maturation is acropetal and slightly asynchronous. The flowers are actinomorphic and have a floral nectary at the base of the filaments. The patterns of inception are simultaneous in the perianth and the androecium. The carpel inception is precocious, prior to the appearance of stamen buds, even in male flowers.

Conclusions:

A. angustissima has particular ontogenetic characteristics, such as the asynchronous maturation of the flower meristems in the inflorescence and the simultaneous emergence of the androecium. It shares with the tribe Ingeae the acropetal inception of the floral meristems in the inflorescence, and with Acacieae and Ingeae the simultaneous inception of the corolla and the precocious inception of the carpel.

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