Irregular vittae and druse crystals in Steganotaenia fruits support a taxonomic affinity with the subfamily Saniculoideae (Apiaceae)

The three-dimensional structure of the vittae and crystals of Steganotaenia araliacea was studied for the first time to allow a rigorous comparison with members of the subfamily Saniculoideae, where these two characters are of diagnostic value. The irregular vittae were found to be branching and anastomosing and druse crystals dispersed in the mesocarp. Both these states are predominant in the Saniculoideae but very rare in Apioideae. In the subfamily Apioideae, regular vittae (vallecular and commissural, or cyclic) are present and druse crystals, if present, occur in the commissural side only. The absence of regular vittae and the presence of irregular vittae and dispersed druse crystals further support the exclusion of Steganotaenia from the subfamily Apioideae but support its hypothesized relation to the Saniculoideae, where large rib ducts combined with irregular vittae (branching or anastomosing) and dispersed druse crystals are typical. This study has led to a better understanding of the taxonomic value of irregular vittae and crystals.