An easy method of identifying herbarium specimens of Najas minor and N. Oguraensis (hydrocharitaceae)

Abstract

Najas minor and N. oguraensis (Hydrocharitaceae) are annual submerged plants and are difficult to distinguish owing to their similarities. While the number of anther locules and the size of the leaf epidermal cells differ between the two species, the anther locules are often difficult to observe on herbarium specimens and the effectiveness of using the size of the leaf epidermal cells as a taxonomic key character is currently unknown. We examined the size of the leaf epidermal cells in living plants and in dried specimens to evaluate the effectiveness of this feature in species identification. We first identified the two species by observing the anther locule number and then compared the size of the leaf cells in fixed and dried specimens. To identify plant fragments, we examined differences in epidermal cell length and width depending on the position of the cells within the plant. The length and width significantly differed in both fixed and dried leaves between the species. In particular, the epidermal cells of N. oguraensis (> 160 μm) were about twice as long as those of N. minor regardless of leaf position. We therefore concluded that cell size, especially length, is a valid method for identifying the species in both fresh and dried condition. This method is effective where precise identifications are necessary, such as in floristic surveys and environmental assessments.