Abstract
Species boundaries between Parthenium hysterophorus L./P. glomeratum Rollins were examined. Our working hypothesis states that the delimitation of these taxa is based on the dissection of a continuous variation pattern from an elevational cline. We chose a 70 km gradient from 300-3500 m in the Province of Salta (Argentina) where both taxa are sympatric. The study was centred in phenetic analyses of morphological data. In addition, foliar and caulinar anatomy, chromosome numbers and karyotype, and sesquiterpene lactone composition were investigated. Transplant experiments were performed, individuais that occur naturally at high elevations were cultivated at lower ones to analyse the phenetic plasticity of some key characters. Our results indicate that based on morphological and anatomical data no group of specimens can be delimited. The main characters used to recognise both species are significantly correlated with the elevation at which they grow, suggesting a clinal variation. Cytological and phytochemical data show that there is variation among the populations and that no discontinuities can be detected to separate them. Accordingly, it is convenient to consider the studied population as belonging to P. hysterophorus , and P. glomeratum as a synonym of that species.
Highlights
Transplant experiments were performed, individuáis that occur naturally at high elevations were cultivated at lower ones to analyse the phenetic plasticity of some key characters
The main characters used to recognise both species are significantly correlated with the elevatum at which they grow, suggesting a clinal variation
El caso del complejo en estudio podría deberse a la disección de un "continuum"; el mismo representaría una variación clinal en un gradiente altitudinal, ya que entre los ejemplares de elevaciones extremas, que tienen las diferencias antes señaladas, se encuentran casos intermedios difíciles de determinar
Summary
Se estudió una población procedente de Salta (Dptos. Chicoana y Cachi), con un total de 45 especímenes (ver tabla 4). La presencia de lactonas en los extractos clorofórmicos de las plantas en dos épocas del año fue determinada en fracciones obtenidas a partir de 500 mg en un sistema cromatográfico de vacío (COLL & BOWDEN, 1986), sobre embudo de vidrio sinterizado Se analizaron las fracciones de cloroformo: acetona (7,5 :7,5 y 5 : 10) por placa analítica de sílicagel G F254, eluyendo con benceno : acetato de etilo (3 : 7) en una dimensión y etanol: agua en segunda dimensión; el revelado se realizó con reactivo de vainillina contra testigos aislados y caracterizados previamente. Se trasplantaron varios individuos del grupo 4 (ejemplar 42 de la tabla 4) y se cultivaron en macetas en la ciudad de Salta, bajo condiciones propias de las plantas del grupo 2, siguiéndose el desarrollo de los individuos por el término de dos años consecutivos (1994-1995)
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