Crystal types and their distribution in the bark of African genistoid legumes (Fabaceae tribes Sophoreae, Podalyrieae, Crotalarieae and Genisteae)

The occurrence and distribution of seven crystal types in 114 bark samples from 25 genera and 91 species, representing all four tribes of African genistoid legumes, are reported. The seven types are prismatic, druse (including irregular crystal clusters), navicular (including truncated navicular, here reported for the first time), spherical crystal cluster, styloid, crystal sand and acicular crystals in sheaf‐like aggregates. Unlike most studies, the elemental composition of the crystals was examined using X‐ray microanalyses. With the exception of acicular crystals, all crystals showed the typical peaks of calcium (sometimes accompanied by small amounts of magnesium). Acicular crystals in sheaf‐like aggregates were composed only of carbon and oxygen, indicating that they are organic and precipitate during drying or after fixation in alcohol. These crystals are found only in the two early‐diverging lineages of Podalyrieae (Cyclopia and Virgilia+Calpurnia clades), consistent with the phylogenetic pattern in the tribe (indicating a secondary loss). Navicular crystals are restricted to Podalyrieae and Crotalarieae. Prismatic crystals in bark are proposed to be the ancestral condition, with multiple losses (or reversals) in Podalyrieae, Crotalarieae and Genisteae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178, 620–632.