Resource allocation below- and above-ground organs and their association to the environment in Mammillaria Haw. (Cactaceae)

When studying plant growth, often the below-ground section is overlooked, and only the above-ground portion is studied. In cacti this bias is emphasized because of the slow growth and high mortality of seedlings in natural, mostly arid environments. Yet, little is known about how cacti invest their resources in building the above- and below-ground sections of the plant. Here we address the issue by studying a range of species in the genus Mammillaria (Cactaceae), and found a diversity of strategies, even in closely related lineages. Taking the forms and shapes of these species, we also proposed growth forms as seedling and as adult plants, discussing that despite being small cacti, Mammillaria species explore an ample diversity of growth forms. Finally, we investigated the prevalence of species to edaphic and landform factors, and found little evidence of a norm among Mammillaria species. Together our results show the interesting diversity in the Mammillaria genus that can be explored for functional and ecological studies in cacti.