Ovule ontogeny in Billbergia nutans in the evolutionary context of Bromeliaceae (Poales)
2014
Fagundes, Natividad Ferreira | de Araujo Mariath, Jorge Ernesto
The infrasubfamilial relations within Bromeliaceae are still not fully understood, especially in Bromelioideae. Billbergia nutans (Bromelioideae) is one of the most widely cultivated bromeliads. This study aims to characterise ovule ontogeny in B. nutans and to review the literature concerning ovules at a family level, to verify useful data for taxonomy and identify the evolutionary scenario of embryological characters within the family. Novel data are recorded for the genus. The ovules of Bromeliaceae are anatropous, bitegmic and crassinucellate, with trizonate ovule primordia, a monosporic development, a linear type of tetrad, callosic cell walls during meiosis, a functional chalazal gynospore, a Polygonum-type gametophyte, the presence of a hypostase, and a dermal origin of the integuments. In B. nutans, the chalazal appendage morphology shows intraspecific variability and might thus not be an appropriate character for taxonomic use. This is the first report on the three-dimensional reconstruction of the female gametophyte of a monocotyledon. Many useful characters are suggested for the taxonomy of Bromeliaceae. The evolutionary scenario of the ovule in the family indicates that the earliest-divergent subfamily, Brocchinioideae, possesses a reduced state of several characters. Among the family, some characters appear homoplasious and might be relevant when applied to lower taxonomic levels. The two-layered integuments and the small number of ovules per carpel are probably plesiomorphic states in Poales.
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