Re-examining the origin and relationship of the Australian octoploid Euphorbia boöphthona using seed morphology

This study aimed to test previous hypotheses about the origin and relationships among the Australian octoploid Euphorbia boöphthona by studying seed morphological characters using scanning electron microscopy. The seed morphologies of the five Australian species of Euphorbia sect. Eremophyton are highly variable and heterogeneous, thus failing to support the previous hypothesis that they are a natural taxon. The diploids E. tannensis and E. parvicaruncula have similar seed shapes, sizes, and surface patterns, suggesting that they are closely related. Although the seed surface of the octoploid E. boöphthona (2n = 56) is uniquely mamillate, the papillae are well developed along the slits of mamilla, very similar to the seed surface of the hexaploid E. stevenii (2n = 42), which shows a distinct papillate pattern. These seed morphological characters support the hypothesis that E. stevenii may be an ancestor of E. boöphthona, as suggested by recent genetic studies.