Cycads are a group of plants in the order Cycadales, comprising ten genera, and with a worldwide distribution. Very few taxonomic revisions are available for the genera in this order, and the present one is intended to provide a revision of the current knowledge in the genus Dioon. The revision was based on bibliographic research and analysis of herbarium specimens, including live specimens found in different botanical gardens and greenhouses. Sixteen species are recognized for the genus. This study includes morphological descriptions, maps with species distribution, line drawings of diagnostic characters, and a key to the species. Detailed taxonomic notes for each species, as well as information on their distribution and habitat is provided, including the uses and common names when available. Fifteen of the total species are distributed in Mexico and one species is found in the border of Honduras and Nicaragua. Therefore, the genus is endemic to Megamexico II.
In this study, we report the observation of potential seed dispersers of the endemic to Mexico and narrowly distributed Ceratozamia norstogii (Zamiaceae). Camera traps were installed in front of two plants of Ceratozamia norstogii and cone phenology until their maturity and disintegration was determined. The female cone of Ceratozamia norstogii has a development of ten months, from the time it emerges until it disintegrates. We were able to identify three stages of cone development: 1) Pre-pollination phase, 2) Pollination phase and 3) Seed maturation phase. Our results support an animal-dispersal hypothesis in Ceratozamia. Three mammals [a mouse (Pteromiscus sp.), a southern spotted skunk (Spilogale angustifrons) and a kinkajou (Potus flavus)] were recorded biting, carrying or removing seeds of Ceratozamia norstogii. The camera traps recorded no evidence of birds or other mammals coming to the cones to feed. Thus, interaction of frugivores with seeds occurs at night. The most frequent visitor was the mouse, followed by the southern spotted skunk and the kinkajou. Significant differences (GLM, p< 0.05) in visitor frequency and time for interaction were found between species. We believe that the mouse is probably the most effective seed disperser for Ceratozamia norstogii. The results presented here have evolutionary implications that can be scaled to the entire genus Ceratozamia. Specifically, short-distance dispersal promotes allopatric speciation in this group of plants.
Reproductive ecology in Ceratozamia has been little studied. In particular, very little is known about seed dispersal. Here we report the observation of seed predators and potential seed dispersers of the endemic to Mexico and narrowly distributed Ceratozamia norstogii (Zamiaceae). Camera traps were installed in front plants of Ceratozamia norstogii and also strobili phenology until their maturity and disintegration was determined. The female strobili of Ceratozamia norstogii has a development of ten months, from the time it emerges until it disintegrates. We identified four stages of strobili development: 1) emergent strobili, 2) young strobili, 3) adult strobili, and 4) mature strobili. Our results support an animal-dispersal hypothesis in Ceratozamia. Three mammals (a mouse, a southern spotted skunk and a kinkajou) were observed consuming or removing seeds of Ceratozamia norstogii. Removal and consumption of mature seeds by frugivorous occur at night. The most frequent visitor was the mouse, followed by the southern spotted skunk and the kinkajou. Significant differences (GLM, P<0.05) in visitor frequency and time for interaction were found between the kinkajou and the rest of the frugivores, but not between the mouse and the skunk. At local scales, seed dispersal by small mammals could be related to the high-density populations of several Ceratozamia species, and at larger scales, related to events of allopatry.
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