Crassula aquatica Stephen M. Young

Crassula aquatica
Stephen M. Young

Class
Dicotyledoneae (Dicots)
Family
Crassulaceae (Stonecrop Family)
State Protection
Endangered
Federal Protection
Not Listed
State Conservation Status Rank
S1
Global Conservation Status Rank
G5

Summary

Did you know?

Water pigmyweed is everywhere and nowhere. It is a very widespread species in the colder regions of Europe and the Western Hemisphere but it is often overlooked because it is so small, has inconspicuous flowers and lives in rarely explored aquatic habitats. In New York it is even harder to see because it occurs in freshwater tidal areas where it is only visible for a few hours each day.

State Ranking Justification

There are two large populations and one very small population which may be extirpated. There are four historical populations which need to be surveyed in more detail but they probably no longer exist.

Short-term Trends

One large population seems to be doing well but more survey work is needed at the remaining two populations to evaluate their current trend. Populations are difficult to survey because of the tidal nature of their habitat and populations could fluctuate dramatically.

Long-term Trends

This species was always very rare in New York occurring in only a few places. Two existing populations are new and one historical population has been rediscovered. The few additional historical populations have not been found.

Conservation and Management

Threats

Overuse of riverside and pond shore habitats as well as invasion of these habitats by Phragmites presents a significant threat to the survival of this species in New York.

Conservation Strategies and Management Practices

Shoreline habitats need to be protected from invasion by Phragmites and other wetland invasive species while also protecting them from overuse by boaters and trampling.

Research Needs

Research is needed to determine if current populations can be augmented by propagation and replanting.

Habitat

Habitat

In New York this species has been found in tidal mud flats, marshes, and rocky shores along the lower Hudson River, and along the banks of an intertidal river on Long Island (New York Natural Heritage Program 2007). Margins of pools and on fresh to tidal shores (Fernald 1970). Muddy shores near the coast, usually in the intertidal zone (Gleason and Cronquist 1991).

Associated Ecological Communities

  • Freshwater intertidal mudflats (guide)
  • Freshwater intertidal shore (guide)
  • Freshwater tidal marsh (guide)
  • Riverine submerged structure

Associated Species

  • Amaranthus cannabinus (salt marsh water-hemp)
  • Callitriche palustris (vernal water-starwort)
  • Cardamine longii
  • Gratiola neglecta (northern clammy hedge-hyssop)
  • Helenium autumnale (common sneezeweed)
  • Limosella australis (Atlantic mudwort)
  • Lindernia dubia
  • Lythrum salicaria (purple loosestrife)
  • Persicaria punctata (dotted smartweed)
  • Pilea fontana (black-fruited clearweed)
  • Plantago maritima
  • Pluchea odorata (salt marsh-fleabane)
  • Pontederia cordata (pickerelweed)
  • Ranunculus repens (creeping butter-cup, creeping crow-foot)
  • Sagina japonica (Japanese pearlwort)
  • Samolus valerandi (water pimpernel, brookweed)
  • Veronica peregrina

Range

New York State Distribution

Water pygmyweed is found in New York only on Long Island and the Lower Hudson Valley, historically to as far north as Ulster County.

Global Distribution

Water Pigymyweed has a widespread but scattered distribution in North America (and is found in Eurasia as well). It occurs in Alaska and all the Canadian Provinces apart from Nunavut, Alberta, Manitoba, and Saskatchewan. In the U.S. its distribution includes the northeastern states from New England as far south as Maryland, the Gulf Coast and lower Mississippi Valley, disjunct to Minnesota, and along the Pacific Coast and some of the Rocky Mountain states.

Best Places to See

  • Iona Island (Rockland County)

Identification Comments

General Description

Water pigmyweed is a small and low-growing (2-10 cm), succulent, annual herb. The leaves are opposite, linear, and less than 1 cm long. The flowers have 4 (or sometimes 3) white petals about 1 mm long. The fruits form round, bluish-green clusters in the axils of the leaves.

Best Life Stage for Proper Identification

This species is best identified when flowering or fruiting.

Similar Species

When collected in fruit or flower, no similar species are extant in New York. Micranthemum micranthemoides, which is presumed to be extirpated in New York, has solitary flowers in the axils of some of the middle leaves and the leaves are not succulent.

Best Time to See

This annual herb species emerges and flowers in June, and the flowers may persist into October.

  • Vegetative
  • Flowering
  • Fruiting

The time of year you would expect to find Water Pigmyweed vegetative, flowering, and fruiting in New York.

Water Pigmyweed Images

Taxonomy

Water Pigmyweed
Crassula aquatica (L.) Schoenl.

  • Kingdom Plantae
    • Phylum Anthophyta
      • Class Dicotyledoneae (Dicots)
        • Order Rosales
          • Family Crassulaceae (Stonecrop Family)

Additional Common Names

  • Pigmyweed

Synonyms

  • Tillaea aquatica L.
  • Hydrophila aquatica (L.) House
  • Tillaeastrum simplex Nutt.
  • Tillaeastrum aquaticum (L.) Britt.

Additional Resources

Best Identification Reference

Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.

Other References

Crow, Garrett E. and C. Barre Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America: A revised and enlarged edition of Norman C. Fassett's a Manual of Aquatic Plants. Volume One: Pteridophytes, Gymnosperms, and Angiosperms: Dicotyledons. The University of Wisconsin Press. Madison, Wisconsin. 536 Pages.

Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.

Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.

New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.

New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.

Reschke, Carol. 1990. Ecological communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation. Latham, NY. 96 pp. plus xi.

Rhoads, Ann F. and Timothy A. Block. 2000. The Plants of Pennsylvania, an Illustrated Manual. University of Pennsylvania Press, Philadelphia, PA.

Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York

Weldy, Troy W. and David Werier. 2005. New York Flora Atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research. University of South Florida]. New York Flora Association, Albany, NY. Available on the web at (http://newyork.plantatlas.usf.edu/).

Links

About This Guide

Information for this guide was last updated on: January 18, 2008

Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Crassula aquatica. Available from: https://guides.nynhp.org/water-pigmyweed/. Accessed March 22, 2019.

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