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Biosystematic analysis of Adiantum vivesii Proctor (Polypodaceae: Adianthoideae), a rare fern endemic to northwestern Puerto Rico

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Abstract
Adiantum vivesii Proctor is a rare fern endemic to the northwestern part of Puerto Rico, known only from its type locality on limestone substrate on privately owned land in the Municipality of Quebradillas. The distribution, abundance, morphology, and cytology of the species were studied to clarify its status as a distinct species or of hybrid or polyploid origen. The population of A. vivesii occupies a total area of 21 m x 10 m; eight sympatric species of Adiantum are found in the immediate area. Following several deep excavations it was concluded that the entire population of A. vivesii is one individual with proliferation by rhizomes. Morphological measurements and light and scanning microscopy were used to describe some parts of A. vivesii and A. tetraphyllum. Morphometric studies were conducted for 22 characters of the species and the possible parent, Adiantum tetraphyllum. Greater variability was obtained within the A. tetraphyllum population, and statistically significant differences between the two species were observed for 17 characteristics. Meiotic studies were inconclusive, but no evident difference in chromosome number was observed between the two species. The spores of A. tetraphyllum showed normal appearance and were rarely abortive, while those of A. vivesii showed greater variability in size and were almost always abortive, suggesting that A. vivesii is a sterile hybrid.
Adiantum vivesii Proctor es un helecho raro y endĂ©mico de la parte noroeste de Puerto Rico, sĂłlo conocido de su localidad tipo en suelos cĂĄrsicos en terrenos privados del Municipio de Quebradillas. La distribuciĂłn, abundancia, morfologĂ­a y citologĂ­a de la especie fueron estudiados para aclarar el estado de la especie como distinta, un hĂ­brido o de origen poliploide. La poblaciĂłn de A. vivesii ocupa un ĂĄrea total de 21 m x 10 m; se encuentran ocho especies simpĂĄtricas de Adiantum en el ĂĄrea inmediata. DespuĂ©s de algunas escavaciones profundas se concluyĂł que la poblaciĂłn de A. vivesii consta de un solo individuo con proliferaciones del rizoma. Medidas morfolĂłgicas y microscopĂ­a de luz y rastreo fueron utilizadas para describir algunas partes de A. vivesii y A. tetraphyllum. Estudios morfomĂ©tricos fueron conducidos para 22 caracteres de la especie y del posible progenitor Adiantum tetraphyllum. Se obtuvo mayor variabilidad dentro de la poblaciĂłn de A. tetraphyllum; 17 caracterĂ­sticas fueron encontradas con diferencias estadĂ­sticamente significativas entre las especies. Estudios meiĂłticos fueron inconclusos, pero no se observĂł una diferencia evidente en el nĂșmero cromosĂłmico entre las dos especies. Las esporas de A. tetraphyllum mostraron una apariencia normal y raramente estuvieron abortivos, mientras que las de Adiantum vivesii mostraron mayor variabilidad en el tamaño y casi siempre estuvieron abortivas, lo cual sugiere que A. vivesii es un hĂ­brido estĂ©ril.
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Date
2000
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Research Projects
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Keywords
Adiantum vivesii Proctor, Fern, Adiantum tetraphyllum
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