Stereoscan model su1510

Seeds were examined by a stereoscopic light microscope (LM) Motic SMZ-168 and a scanning electron microscope (SEM) Hitachi Stereoscan Model Su1510 (10 kv voltage and secondary electron detector). For SEM, three seeds per taxon were randomly selected and washed in distilled water, TWENG detergent (10 drops), 4 % sodium hypochlorite and five minutes of ultrasound. Later, they were fixed in an aluminium porta-sample with adhesive tape and coated with gold. This technique was carried out at the Electron Microscopy Laboratory of the Instituto de Biología de la Universidad Nacional Autónoma de México. For each seed, SEM micrographs were taken in several views: lateral, frontal, apical, and cells of several regions: lateral, hilum-micropylar border, and apical. In the case of seeds of Melocactus perezassoi, it was not possible to take SEM micrographs, and their morphology was evaluated according to the photographs presented by Guiggi (2010) and observations made with LM; the seeds photographed by Guiggi (2010) and those used in this study came from the same population (the only known population for this taxon). Seed morphological characters were analysed using the micrographs obtained and observations in LM of 50 seeds per taxon (or per locality, when a taxon was sampled from more than one locality). Observations in LM allowed checking of all characters analysed in SEM.