I hate to be the bearer of bad news, but we found a new invasive last week. One of our crews saw a plant that they had not seen before and I asked them to bring me a sample. We sent the sample to CDFA and they have confirmed our fears that it was Spongeplant. It is also called Smooth frogbit as well. Below I have posted literature on why we should be vigilant. The population we found was near Brannan island and I have been informed that some of it blew out in this last storm. There is a native sponge plant and I will post pictures of both species to help you tell the difference. Thanks for your help and I am hoping this is an isolated population and there is no more to be found. It is very similar to hyacinth in it's growth rate and reproduction.
Limnobium spongia and L. laevigatum are a bit more difficult to distinguish. The most reliable characteristic is stamen number. Generally there are six in L. laevigatum and 9-12 in L. spongia. In the absence of flowering material leaf tip shape is useful; the leaf tip is more or less acute in L. spongia but decidedly rounded in L. laevigatum. Otherwise these two species are quite similar appearing and both have the same aggressive habit when introduced into areas without natural controls.
Limnobium are aquatic perennial herbs which grow in dense floating mats or rooted in mud on wetland edges. The flowers are held above water and pollination is probably via wind currents. The seeds are shed above water, but germinate submerged and the seedlings float to the surface where they grow rapidly (Cook & Urmi-Konig op. cit.). Although occurring up to 2800 meters in elevation, Limnobium laevigatum is marginally hardy in California, however it survived temperatures to approximately –4°C (25°F) in the San Francisco Bay Area in the 1998-1999 winter. Limnobium spongia is hardy to temperatures well below those known in low elevation California. Both reproduce rapidly by both seed and stolons, quickly filling newly colonized sites with both clones and new individuals, and both are often considered pestiferous even in their native ranges. Limnobium spongia sensu stricto has become established in several states west of its native range, although at present only Limnobium laevigatum has been found introduced into the wild in California, likely because it is the only one currently sold as an ornamental. Individual seeds are covered with small spinules and the seeds when shed are contained in a gelatinous mass; both forms readily attach to watercraft and if they should become established in navigable waterways are likely to spread rapidly and widely.
Pictures: Limnobium spongia is the species of concern
http://www.lucidcentral.org/keys/aq..._Plants/Media/Html/Fact_sheets/limnobium.html
Limnobium spongia and L. laevigatum are a bit more difficult to distinguish. The most reliable characteristic is stamen number. Generally there are six in L. laevigatum and 9-12 in L. spongia. In the absence of flowering material leaf tip shape is useful; the leaf tip is more or less acute in L. spongia but decidedly rounded in L. laevigatum. Otherwise these two species are quite similar appearing and both have the same aggressive habit when introduced into areas without natural controls.
Limnobium are aquatic perennial herbs which grow in dense floating mats or rooted in mud on wetland edges. The flowers are held above water and pollination is probably via wind currents. The seeds are shed above water, but germinate submerged and the seedlings float to the surface where they grow rapidly (Cook & Urmi-Konig op. cit.). Although occurring up to 2800 meters in elevation, Limnobium laevigatum is marginally hardy in California, however it survived temperatures to approximately –4°C (25°F) in the San Francisco Bay Area in the 1998-1999 winter. Limnobium spongia is hardy to temperatures well below those known in low elevation California. Both reproduce rapidly by both seed and stolons, quickly filling newly colonized sites with both clones and new individuals, and both are often considered pestiferous even in their native ranges. Limnobium spongia sensu stricto has become established in several states west of its native range, although at present only Limnobium laevigatum has been found introduced into the wild in California, likely because it is the only one currently sold as an ornamental. Individual seeds are covered with small spinules and the seeds when shed are contained in a gelatinous mass; both forms readily attach to watercraft and if they should become established in navigable waterways are likely to spread rapidly and widely.
Pictures: Limnobium spongia is the species of concern
http://www.lucidcentral.org/keys/aq..._Plants/Media/Html/Fact_sheets/limnobium.html
