Sterculiaceae of Paraguay. I. <i>Ayenia, Byttneria, Guazuma, Helicteres, Melochia</i> and <i>Sterculia</i>

The taxonomic revision of the Sterculiaceae family in Paraguay is presented here, including 56 species and 4 varieties, a total of 59 taxa three of which are endemic. They belong to 7 genera, the same that grow in Argentina, with a variable number of species, ranging from 1 like in&nbsp;Sterculia&nbsp;and&nbsp;Guazuma&nbsp;to 16 such as&nbsp;Byttneria&nbsp;andMelochia. The family is distributed along all the area in very diverse habitats, like gallery forests, fertile lands, but also on calcarate, saltpetrous or sandy soils. The habit is generally shrubby to sub-shrubby, rarely arborescent or climbing. The plants are unarmed or spinose such in some&nbsp;Byttneria&nbsp;species. The project to revise this family stimulated the attention in the field work. As result was foundAyenia magna, member of the section&nbsp;Cybiostigma. Its more southern area was Trinidad in the coast of Venezuela, and now it has been found at Cerro Le&oacute;n, in the north of western Paraguay. Another interesting finding is&nbsp;Ayenia spinulosa, which has been only known by the type specimen. This species grows on calcarate soils of the Concepci&oacute;n department. A generous amount of specimens make possible that this taxa can be represented in many herbaria of the world. The Sterculiaceae flowers are always small, usually agglomerate at the leafs axils, and in many cases morphologically complex. The petals are reddish or violet, rarely yellow like inWaltheria, or white. In&nbsp;Melochia&nbsp;it can be longistyle, brevistyle or mesostyle. The leaves are petiolate, estipulate, with stellate, single or glandular hairs. The appearance of the plants and the indument are similar to many Malvaceae, due to which it is necessary to examine this family at the herbaria. The anthers are dithecal and enlarged in Sterculiaceae, while in Malvaceae are monothecal and rounded. The text includes the description, synonymy and illustration of each taxon, keys to distinguish each one and its geographic distribution represented on 11 maps. The illustrations of some genera were taken from previous studies, but theMelochia&nbsp;drawing have been prepared for the present revision, which it is interesting because the author of the monograph do not included illustrations of each taxon.