Martiodendron Gleason is a South American genus with five species of trees, belonging to the tribe Cassieae, subtribe Dialiinae (Leguminosae, "Caesalpinioideae”). Dialiinae has 17 genera that form a clade whose generic relationships are not highly resolved. This paper describes and illustrates the early development and seedling morphology of Martiodendron excelsum. We review the current state of knowledge of seedling morphology in Dialiinae, in order to evaluate its systematic relevance at a generic level. Seeds of M. excelsum were collected from wild populations in Roraima State, Brazil. Martiodendron excelsum has phanerocotylar, epigeal seedlings with storage cotyledons, with stipulate and 1-foliolate eophylls at the first three nodes. Seedling morphology data are potentially useful for diagnosing genera in Dialiinae. Martiodendron and all other remaining genera can be distinguished from each other by the variation in seedling morphological groups, as well as length-width ratio of cotyledons, phyllotaxis and leaflet number of the first and second eophylls, ratio of hypocotyl length to epicotyl length, and elongation of the first eophyllar internode. In addition, within Leguminosae, the predominance of 1-foliolate eophylls in most genera of Dialiinae is only comparable among seedlings of Papilionoideae taxa.
Cassieae; post-seminal development; Roraima; taxonomy
