For a great online site for pictures, fact sheets, and keys to many freshwater species in the aquarium trade, try:
Winterton, S.L., Scher, J.L., Burnett, J., and Redford, A.J. 2018. Aquarium and Pond Plants of the World, Edition 3. USDA APHIS Identification Technology Program (ITP) and California Department of Food and Agriculture. Sacramento, CA. [3/10/2023]
Instructions for using their key: https://idtools.org/appw/index.cfm?pageID=3099
Mangroves form forests in the salty shallows where sea meets land, and are critical breeding grounds for all sorts of sea life, as well as being crucial for erosion control. Scientists argue over how to define what is and is not a mangrove, but in general, these are woody plants that have a very specific set of adaptations for flourishing in their salty, wet, shifting habitat (Barik & Chowdhury, 2014). These include visually striking root modifications, such as roots that grow up out of the wet soil for better access to oxygen (pneumatophores) and other above-ground roots to broaden the base of the tree and provide stability in the face of waves and shifting soil (ex. stilt roots and knee roots). The leaves have numerous adaptations for coping with water stress (xerophyllous) and glands to excrete excess salt. The fruit often germinate while still on the mother tree (viviparous) and then are water dispersed once they fall off. Despite this long list of unique traits, mangroves belong to several different families of plants, and so are a neat example of convergent evolution, where similar environments select for similar traits in unrelated organisms.
Because mangroves are woody, they are beyond the scope of this herbaceous water plant project, but there is a Mangroves of the World project ( https://www.inaturalist.org/projects/mangroves-of-the-world ) if you need a closer look at these species.
If you want a closer look at their viviparous propagules (or other weird seeds or fruit washed up on a beach), the Drift Seeds and Sea Beans project ( https://www.inaturalist.org/projects/drift-seeds-and-sea-beans ) may also be worth a visit.
References:
Barik, J., & Chowdhury, S. (2014). True mangrove species of Sundarbans delta, West Bengal, eastern India. Check list, 10(2), 329-334. https://doi.org/10.15560/10.2.329
The land plants, from mosses to flowering plants, all share an aquatic ancestor that left the water to conquer new territory. Today's aquatic plants all had terrestrial ancestors that changed their minds: they left the land and re-adapted to life in the water.
Among the land plants, 103 families and 440 genera include aquatic species (Cook 1999). Only about 2% of angiosperm species are aquatic, but across the angiosperms, aquatic lifestyles are estimated to have evolved at least 200 times (Cook 1999). Add in some aquatic ferns and lycophytes, and the aquatic tracheophytes are a fascinatingly diverse group.
Useful references:
Cook CDK. 1999. The number and kinds of embryo-bearing plants which have become aquatic: a survey. Perspectives in Plant Ecology, Evolution and Systematics 2: 79–102. https://doi.org/10.1078/1433-8319-00066
Cook CDK. 1990. Aquatic Plant Book. SPB Academic Publishing, The Hauge, The Netherlands. 228 pages.
Meseguer AS, Carrillo R, Graham SW, Sanmartín I. 2022. Macroevolutionary dynamics in the transition of angiosperms to aquatic environments. New Phytologist. 2022 Mar 16. https://doi.org/10.1111/nph.18100
Philbrick CT, Les DH. 1996. Evolution of aquatic angiosperm reproductive systems. Bioscience 46(11): 813-26.
Rataj K, Horeman TJ. 1977. Aquarium Plants: Their Identification, Cultivation and Ecology. TFH Publications, New Jersey, USA.
