CMT: This species as described by Bremekamp is characterized by its oblanceolate, ternate to verticillate leaves; lax corymbiform inflorescences with the flowers all pedicellate; medium-sized corollas (for Chassalia); narrowly ovoid fruits; and distribution at middle elevations in in humid forests in the eastern region. This species name was incorrectly spelled by Bremekamp, as "catati". Several other Chassalia species also have ternate leaves of similar shape but differ in their flowers that are mostly or all sessile and their ellipsoid to subglobose fruits, in particular Chassalia bojeri with sessile flowers arranged in small heads or glomerules. Also similar are several species with pedicellate flowers and opposite leaves, in particular Chassalia assimilis and Chassalia betamponensis.
Chassalia catatii is similar to Chassalia quaternifolia, Chassalia ternifolia, and Chassalia verticillata in leaf arrangement, pedicellate flowers, corolla size and degree of lobing, and the relatively narrow, somewhat large fruits, and these may not be distinct. These were separated by Bremekamp based on number of leaves per node and leaf size and shape. However those features vary on individual stems and apparently in populations: in particular, a broad ange of variation is found in specimens from Ranomafana, which seem to represent a single species. Here Chassalia catatii is separated somewhat arbitrarily by its longer, relatively more narrow leaves and shorter pedicels, vs. generally shorter and broader leaves and longer pedicels in Chassalia ternifolia. Chassalia quaternifolia also has relatively long narrow leaves but here only plants from Toliara are included in that species, and only plants from further north in Chassalia catatii.
Chassalia catatii has been extensively confused in herbarium identifications with the more commonly collected species Chassalia pentachotoma. This other species generally has similar orange or orange-brown drying color, but can be separated by its opposite leaves and pyramidal inflorescences with the flowers in dichasial cymes, with some flowers sessile or subsessile and others separated on axes or pedicellate.
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