Fruit and seed morphometry and seed structure of the potentially invasive Calotropis procera (Aiton) W.T. Aiton (Apocynaceae)

Abstract

Background: Calotropis procera is a plant native in the tropics and subtropics of Asia and Africa. In Mexico, its presence is now registered in Yucatán, Quintana Roo and Oaxaca. Questions and / or Hypotheses: Fruit and seed morphometry vary among places where it is native or exotic? Are seed structures well identified in Calotropis procera? Studied species: The exotic Calotropis procera has been already reported in several states in Mexico, however, information about its reproductive biology in Mexican populations is scarce.   Studied site and dates: Fruits were collected in Oaxaca, Mexico in September 2019. Methods: We obtained fruit and seed morphometric data and seed images with microscopy. Results: The fruits are green and ovoid. The average number of seeds per fruit is 364 ± 86 (SD). The seed is brown and flattened dorsoventrally. The length of the seeds is 8.37 ± 0.413 mm, the width is 5.01 ± 0.39 mm, and the weight is 10.5 ± 7.86 mg. The position of the hilum and the micropyle is reported and the occurrence of two types of trichomes on the testa. We suggest that the protrusion on the ventral surface of the seed is the raphe. Conclusions: From data obtained we concluded that fruit and seed characteristics are well conserved in this species. We confirmed the position of the hilum and micropyle and reported the presence of two types of trichomes in the testa. Location of the raphe is suggested, providing information that may be useful for future taxonomic studies.