VARIATION IN NUTLET MORPHOLOGY OF LIMNANTHES

Morphological features of nutlets of all members of the genus Limnanthes were examined by light and scanning electron microscopy (SEM). Eight distinct nutlet types are recognized on the basis of presence or absence, size, shape, density, and color of tubercles and associated filamentous or globular background structures. Some taxa (e.g., L. macounii, L. bakeri) display only one nutlet type, some (e.g., L. floccosa floccosa) have different types in different populations, and others (e.g., L. alba, L. striata) have two or more types within populations. Four classes of nutlets are designated as subtypes on the basis of their forms varying between the eight types recognized. The relationships among various taxa on the basis of nutlet types are schematically diagrammed and compared with other classification schemes. Results suggest that the proposed details of nutlet morphology should be considered in an identification key. Preliminary evidence indicates that certain highly sculptured (tuberculate) nutlet types with large surface areas occur more often in wetter habitats and that variation in this trait in different Limnanthes species might be adaptively associated with geographical distribution patterns.