The Cycadales are a group of significant global conservation concern and have the highest extinction risk of all seed plants. Understanding the synchronisation of reproductive phenology of Cycadales may be useful for conservation by enabling the targeting of pollen and seed collection from wild populations and identifying the window of fertilisation to aid in the cultivation of Cycadales. Phenological data for 11 species of Zamia were gathered from herbarium specimens. Four phenological characters were coded with monthly character states. DNA was isolated and sequenced for 26S, CAB, NEEDLY, matK and rbcL, and a simultaneous phylogenetic analysis of phenology and DNA sequence data was carried out. Three major clades were recovered: a Caribbean clade, a Central American clade and a South American clade. Eight species showed statistically significant synchronisation in microsporangiate and ovulate phenological phases, indicating the time of fertilisation. Close reproductive synchronisation was consistently observed throughout the Caribbean clade (statistically significant in four of five species) but was less consistent in the Central American clade (statistically significant in one of two species) and South American clade (statistically significant in three of four species). Ultimately, phenology is shown to be a potential driver of speciation in some clades of Zamia and in others to be a potential barrier to hybridisation.

Somatic chromosomes at mitotic metaphase of two species and two undescribed populations of Bowenia, and Stangeria eriopus, which were classified in Stangeriaceae, Cycadales, were compared using the standard aceto-orcein staining method. All Bowenia taxa showed a chromosome number of 2n = 18, while S. eriopus showed a chromosome number of 2n = 16. The chromosome number of 2n = 18 in B. ‘Kuranda’ is reported for the first time. The present karyotype analysis indicates that B. ‘Kuranda’ and another undescribed taxon, B. ‘Tinaroo’, are cytotaxonomically closer to B. spectabilis than B. serrulata, and that the karyotype of Stangeria is unlikely to have been derived from that of Bowenia by a simple chromosomal change such as centromeric fission and deletion.