Najas guadalupensis

Najas guadalupensis, the southern naiad, is a submersed aquatic plant widespread across the American continent, where it inhabits lakes, rivers and canals. According to “Flora of North America” there are four subspecies. Three of them (N. guadalupensis subsp. floridana, subsp. muenscheri, subsp. olivacea) are restricted to North America, whereas N. guadalupensis subsp. guadalupensis also occurs in Central and South America and on the Caribbean islands.

The southern naiad has been kept in aquariums for many years and is probably by far the most common and best-known Najas species in the aquarium hobby. Its English name “Guppy grass” reflects the popularity of this undemanding aquatic plant, which is often used in breeding tanks for fish and invertebrates. It is more likely to be obtained from other hobbyists, e.g. at aquarium fairs, than from specialist retailers. This naiad may not be particularly popular with planted-tank enthusiasts and aquascapers, however, because the stems are very brittle and the detached, drifting shoot fragments settle uncontrollably in all sorts of places in the aquarium, so that this fast-growing plant can become quite a nuisance “weed”.

While many other Najas species have distinctly toothed leaves, the leaf margins of N. guadalupensis appear entire at first glance, but are in fact set with many tiny teeth that are visible under magnification. The southern naiad closely resembles the slender naiad (Najas flexilis), which occurs in North America and Europe and, according to the Red List of 1996, is threatened with extinction in Germany. The two species differ mainly in their seeds: in N. flexilis they are yellowish, smooth, glossy and widest above the middle, whereas N. guadalupensis has spindle-shaped, yellowish white, purple-tinged seeds with a dull and distinctly areolate surface.

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