Chromosome Number and Classification in Hydrophyllaceae

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Abstract
A 20-year investigation of chromosome number in all 18 genera and more than 200 species (perhaps two-thirds of the total) of the plant family Hydrophyllaceae has not resulted in the discovery either of a single base-number for the family or of a primitive genus, and it has not settled the question as to whether or not the famliy is a strictly natural one. Chromosome number has confirmed the general grouping, earlier proposed by various authors on morphological grounds, of such genera asHydrophyllum, Pholistoma, Nemophila, andEllisia (Constance 1939a) ;Eriodictyon, Nama, Lemmonia, andTurricula; andHesperochiron andTricardia. It has also revealed the occurrence of several polyploid series, and has exposed certain trends in morphology, such as reduction in the number of ovules and the specialization of annual habit from perenniality. Within certain genera, especially the large genusPhacelia, chromosome number has been of considerable assistance both in permitting a more natural grouping of species, and in shedding some light on interrelationships of species and species-groups and their probable phylogeny.

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