- Scientific name: Crassula aquatica (L.) Schönland
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Threatened (MA Endangered Species Act)
Description
Shore pygmy-weed (Crassula aquatica) is a tiny, annual, fleshy herbaceous aquatic plant that grows on coastal or freshwater shores. A member of the stonecrop family (Crassulaceae), these plants have tiny, single white flowers that appear in leaf axils from July through September. These inconspicuous plants grow either in low-spreading, sprawling mats on mud flats or elongated and partially submerged in water.
Shore pygmy-weed’s slender stems arise from the plant’s base, then branch and curve upward (to 2-6 mm [0.08-0.24 in] high in its low form and up to 10 cm [4 in] in its elongated form). The leaves are fleshy, entire, and linear (2-7 mm [0.08-0.28 in] long). They are arranged oppositely on the stem, and are not merely sessile, but actually join at the stem to form a boat-shaped cup at the point of attachment. Inconspicuous white or greenish-white flowers (1 mm [0.04 in] wide) emerge singly from the leaf axils on short stalks. Each flower has (usually) four narrow petals. Flower stalks elongate as the fruits mature into follicles containing 8 to 10 seeds. Minute, brown, oblong-shaped seeds have pits between striated lines on their surfaces that can be seen under magnification.
Other small, low-growing shore plants with tiny opposite leaves that could be confused with the shore pygmy-weed in Massachusetts are the waterworts (Elatine spp.), and the aquatic form of northern dwarf St. John’s-wort (Hypericum boreale forma callitrichoides). However, the leaves of these other plants are not fleshy, nor are they linear (they are broader in shape). Also, the leaves do not form a boat-shaped cup at the point of attachment along the stem as in the shore pygmy-weed.
Life cycle and behavior
These plants have tiny, single white flowers that appear in leaf axils from July through September.
Population status
Shore pygmy-weed is listed under the Massachusetts Endangered Species Act as threatened. All listed species are protected from killing, collecting, possessing, or sale and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors. Seven populations have been verified extant since 1999 in Bristol, Dukes, Franklin, Nantucket, and Plymouth Counties. In the past, it was also found in Hampshire County as well.
Distribution and abundance
Shore pygmy-weed is known from 23 states across America, in a sporadic pattern, with many miles between occurrences. In the north, the species is found in all New England states, New York, Delaware, Pennsylvania, and Maryland. Westward, it is found in Minnesota and in the Pacific coastal states of Washington, Oregon, California, and Alaska. Its southern range encompasses Georgia, Alabama, Louisiana, Arkansas, Oklahoma, Texas, New Mexico, and Utah. In New England, shore pygmy-weed is critically imperiled in Connecticut and New Hampshire, imperiled in Maine and Massachusetts, and possibly extirpated in Vermont. It is not known from Rhode Island (NatureServe 2025 and Haines 2011).
Distribution in Massachusetts
1999-2024
Based on records in the Natural Heritage Database
Habitat
Shore pygmy-weed occurs along both fresh and tidal brackish water, including such habitats as the margins of freshwater ponds and rivers, and on tidal mud flats or along salt ponds. This species favors sandy and/or muddy wet soil. In freshwater habitats, the shore pygmy-weed grows among low herbaceous plants such as mud hedge-hyssop (Gratiola neglecta), water purslane (Ludwigia palustris), low cudweed (Gnaphalium uliginosa), and Pennsylvania smartweed (Persicaria pensylvanica). In brackish habitats, it has been found growing with lilaeopsis (Lilaeopsis chinense), water-pimpernel (Samolus valerandi ssp. parviflorus), and Atlantic mudwort (Limosella australis).
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Threats
This species is associated with aquatic habitats so threats include those that alter hydrologic regimes, including water extraction and climate change.
Conservation
As for many rare species, exact needs for management of shore pygmy-weed are not known. However, preserving the integrity of its habitat is a logical first step. This may involve restricting recreational shore use to avoid trampling and compaction of shorelines and maintaining existing hydrology. Field notes suggest that populations may decline with high water levels, and that the natural opening and flushing of salt pond habitats once every year or two may benefit populations. Further research is needed to determine precise ecological requirements of this species.
References
Haines, A. 2011. Flora Novae Angliae – a Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England. New England Wildflower Society, Yale Univ. Press, New Haven, CT.
NatureServe. 2025. NatureServe Network Biodiversity Location Data accessed through NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. Accessed: 5/23/2025.
Contact
| Date published: | April 14, 2025 |
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