Morfologia e desenvolvimento floral em Croton L. e Astraea Klotzsch (Euphorbiaceae sensu stricto)
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Data
2010-06-28
Autores
Paula, Orlando Cavalari de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Croton agrupa cerca de 1.200 espécies portadoras de flores bissexuais e representa um grupo complexo, sob o ponto de vista taxonômico e morfológico. Astraea, recentemente separada de Croton e com quem divide inúmeras características morfológicas, é um gênero pouco estudado. A natureza dos verticilos florais, especialmente nectários e estruturas filamentosas das flores pistiladas, é um assunto bastante controvertido, nos dois gêneros. Estudos com as flores de Croton mostram o desenvolvimento do óvulo e da semente e outros apenas descrevem a morfologia do grão de pólen maduro. Entretanto, para o gênero Astraea nada se conhece até o momento. Analisando o desenvolvimento, a vascularização e a morfologia de flores estaminadas e pistiladas, de Croton e Astraea, verificou-se que as estruturas filamentosas das flores pistiladas correspondem às pétalas presentes nas flores estaminadas, e que os nectários representam estames transformados; observou-se, inclusive, que flores pistiladas podem desenvolver estames em substituição aos nectários. Também foi possível apontar caracteres que apóiem a segregação de Astraea e Croton, embora os dois gêneros compartilhem inúmeras características morfológicas. O estudo do desenvolvimento da antera e óvulo de duas espécies de Astraea e de sete de Croton mostrou a ocorrência de cristais estilóides, no tapete, e de idioblastos portadores de drusa, no endotécio; mostrou também, a presença de óvulos com os dois tegumentos de origem epidérmica e a diferenciação de megásporo funcional em posição micropilar. Esses aspectos, descritos pela primeira vez para a família, precisam ser melhor investigados a fim de se determinar sua ocorrência e distribuição, dentro do grupo, e avaliar melhor seu potencial taxonômico.
Croton comprises approximately 1,200 species with bisexual flowers and is a taxonomically and morphologically complex group. Astraea, which was recently separated from Croton and shares innumerous morphological characteristics, is still a poorly studied genus. The nature of the floral whorls, especially the nectaries and the filamentous structures of the pistillate flowers, is a controversial subject in both genera. Some studies with Croton flowers have examined the development of ovules and seeds, while others have only described the morphology of mature pollen grains. Very little is currently known about Astraea. Analyses of the development, vascularization, and morphology of the staminate and pistillate flowers of Croton and Astraea demonstrated that the filamentous structures of the pistillate flowers represent transformed petals, and that nectaries represent transformed stamens in pistillate flowers; stamens were occasionally observed in place of nectaries. Many characteristics were observed that support the segregation of Astraea from Croton, although the two genera do share numerous morphological features. An examination of the development of the anthers and ovules of two species of Astraea and seven species of Croton demonstrated the presence of styloid crystals in the tapetum as well as idioblasts with druses in the endothecia; ovules with two teguments of epidermal origin and the differentiation of a functional megaspore in a micropylar position were also observed. These aspects, described here for the first time for the family, need to be further investigated to determine their occurrence and distribution within the taxon, and to evaluate their taxonomic potential.
Croton comprises approximately 1,200 species with bisexual flowers and is a taxonomically and morphologically complex group. Astraea, which was recently separated from Croton and shares innumerous morphological characteristics, is still a poorly studied genus. The nature of the floral whorls, especially the nectaries and the filamentous structures of the pistillate flowers, is a controversial subject in both genera. Some studies with Croton flowers have examined the development of ovules and seeds, while others have only described the morphology of mature pollen grains. Very little is currently known about Astraea. Analyses of the development, vascularization, and morphology of the staminate and pistillate flowers of Croton and Astraea demonstrated that the filamentous structures of the pistillate flowers represent transformed petals, and that nectaries represent transformed stamens in pistillate flowers; stamens were occasionally observed in place of nectaries. Many characteristics were observed that support the segregation of Astraea from Croton, although the two genera do share numerous morphological features. An examination of the development of the anthers and ovules of two species of Astraea and seven species of Croton demonstrated the presence of styloid crystals in the tapetum as well as idioblasts with druses in the endothecia; ovules with two teguments of epidermal origin and the differentiation of a functional megaspore in a micropylar position were also observed. These aspects, described here for the first time for the family, need to be further investigated to determine their occurrence and distribution within the taxon, and to evaluate their taxonomic potential.
Descrição
Palavras-chave
Anatomia vegetal, Embriologia, Nectarios, Estaminódios, Pétalas, Staminodes, Petals
Como citar
PAULA, Orlando Cavalari de. Morfologia e desenvolvimento floral em Croton L. e Astraea Klotzsch (Euphorbiaceae sensu stricto). 2010. 61 f. Tese (doutorado) - Universidade Estadual Paulista, Instituto de Biociências de Rio Claro, 2010.