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Riverweed Podostemum ceratophyllum plants Photo credits: Stephen M. Young Scientific Name Podostemum ceratophyllum Michx. Family Name Podostemaceae Did you know? This is the only member of this genus and family that occurs in North America. The genus is confined to the New World (Philbrick and Novelo 2004). The genus name Podostemum comes from the greek words for foot and stamen and is in reference to the stamens appearing "raised on a stalk by the side of the ovary" (Fernald 1970). The specific epithet ceratophyllum means horn-leaf (Fernald 1970) and may be in reference to the narrow stiff leaves of this species. Summary Protection Threatened in New York State, not listed federally. This level of state protection means: listed species are those with: 1) 6 to fewer than 20 extant sites, or 2) 1,000 to fewer than 3,000 individuals, or 3) restricted to not less than 4 or more than 7 U.S.G.S. 7 ½ minute topographical maps, or 4) listed as threatened by U.S. Department of Interior. Rarity G5, S2 A global rarity rank of G5 means: This species is demonstrably secure globally, though it may be quite rare in parts of its range, especially at the periphery. A state rarity rank of S2 means: This plant is threatened/imperiled in New York because of rarity (typically 6-20 populations or few remaining individuals) or is vulnerable to extirpation from New York due to biological factors. Conservation Status in New York There are 16 known extant populations and 8 populations which have not been seen in recent years and are considered historical. Many of the populations are clustered along particular rivers. Habitat is somewhat limited for this species but certainly not rare. NYNHP Conservation Guide - Riverweed (Podostemum ceratophyllum) Short-term Trends Fifteen out of the 16 known extant populations have first been documented in the past 30 years. This would seem to point to an increase in this species but since this species is often overlooked, resembles algae, and grows in habitat that make it difficult to detect, it is equally possible that these "new" populations were simply overlooked in the past. Overall, short term trends are not clear but probably are at least stable. Long-term Trends No population of this species is known to have become extirpated. Eight populations have not been seen in over 25 years. These populations may still be extant, as targeted surveys at these populations have not been conducted. The habitat for this species may have decreased some in the past 100+ years as rivers and streams were developed and/or polluted. Overall long term trends are not clear. Conservation and Management Threats Some of the streams where this species occurs may be used for a water source. This development could result in a change to the stream that would make the habitat less suitable for riverweed. Other populations are threatened by water quality deterioration as a result of development, agriculture, and run off from a sewage treatment plant (New York Natural Heritage Program 2007). Negative impacts on rivers including siltation, nutrient pollution, and dam building have been considered threats to this species (Quiroz et al. 1997 in Philbrick and Novelo 2004). Conservation Strategies and Management Practices Water quality of the rivers where this species occurs, should be protected. Research Needs Surveys to historical populations are needed to determine if these populations are still extant. Habitat Riverweed grows submerged (up to 75+ cm deep) to seasonally exposed on cobbles and bedrock substrate in fast flowing, relatively large streams or rivers. It often occurs in rapids (New York Natural Heritage Program 2008). Fast-moving streams, especially rapids (Crow and Hellquist 2000). In rapidly flowing water (Gleason and Cronquist 1991). On rocks in streams (Fernald 1970). Associated Ecological Communities Confined River The aquatic community of relatively large, fast flowing sections of streams with a moderate to gentle gradient. Rocky Headwater Stream NYNHP Conservation Guide - Riverweed (Podostemum ceratophyllum) 2 The aquatic community of a small- to moderate-sized perennial rocky stream typically with a moderate to steep gradient, and cold water that flows over eroded bedrock, boulders, or cobbles in the area where a stream system originates. Associated Species Cladophora sp. Identification Comments Riverweed is an olive-green, aquatic plant of firm texture that grows in streams and rivers attached to rocks. It resembles seaweed, alga, or moss and attaches to rocks by fleshy disks. The stems are 2-30 cm long and often branched. The leaves are very narrow and divided into numerous linear lobes. The flowers are small, not showy, and scattered along the stems (Fernald 1970, Gleason and Cronquist 1991, Philbrick and Novelo 2004). Best Life Stage for Identifying This Species It is easiest to identify this plant when it is in flower or fruit although vegetative material, when not confused with alga or moss, is also relatively easy to identify. The Best Time to See Flowers and/or fruits are present from mid-June through early October. Since this species often grows submerged in rapids and fast moving water it can be difficult to spot. Therefore, the best time to survey for this species is between mid-June and early October and when water levels are low. Vegetative Flowering Fruiting Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec The time of year you would expect to find Riverweed in New York. Similar Species This species is perhaps superficially similar to alga and moss but can be distinguished from both by its true although minute flowers, its firm texture, fleshy disks (which attach to the substrate), and stipule-like appendages at the bases of the leaves. The latter three characters will also help separate this species from other aquatic vascular plants. Conservation Comments When Michaux (1803) described this genus he used the spelling "Podostemum" in the text and then in a plate illustrating Podostemum ceratophyllum he used the spelling "Podostemon". It appears that Michaux's Podostemon was in error (Sprague 1933) and the family Podostemaceae (based on Podostemum) has been conserved as the correct NYNHP Conservation Guide - Riverweed (Podostemum ceratophyllum) 3 spelling (McNeill et al. 2006). Podostemon is therefore considered an orthographic variant and is to be replaced by the correct spelling Podostemum. Taxonomy Kingdom Plantae Phylum Anthophyta Class Dicots (Dicotyledoneae) Order Podostemales Family Podostemaceae Additional Common Names Horn-leaved riverweed River-moss Threadfoot Synonyms Podostemon ceratophyllum (Michaux) Additional Resources Links New York Flora Atlas http://www.newyork.plantatlas.usf.edu/Plant.aspx?id=2412 USDA Plants Database http://plants.usda.gov/java/nameSearch?mode=sciname&keywordquery= PODOSTEMUM+CERATOPHYLLUM NatureServe Explorer http://natureserve.org/explorer/servlet/NatureServe?searchName=PODOSTEMUM+CERA TOPHYLLUM Google Images http://images.google.com/images?q=PODOSTEMUM+CERATOPHYLLUM 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: Dicotyledon Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp. Gleason, Henry A. 1952. The New Britton and Brown Illustrated Flora of the Northeastern United States and Canada. 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. NYNHP Conservation Guide - Riverweed (Podostemum ceratophyllum) 4 Haines, Arthur and Thomas F. Vining. 1998. Flora of Maine. A Manual for Identification of Native and Naturalized Vascular Plants of Maine. 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. Keys, Jr.,J.; Carpenter, C.; Hooks, S.; Koenig, F.; McNab, W.H.; Russell, W.;Smith, M.L. 1995. Ecological units of the eastern United States - first approximation (cd-rom), Atlanta, GA: U.S. Department of Agriculture, Forest Service. GIS coverage in ARCINFO format, selected imagery, and map unit tables. McNeill, J., F.R. Barrie, H.M. Burdet, V. Demoulin, D.J. Hawksworth, K. Marhold, D.H. Nicolson, J. Prado, P.C. Silva, J.E. Skog, J.H. Wiersema, and N.J. Turland (Editors). 2006. International Code of Botanical Nomenclature (Vienna Code) adopted by the Sev Michaux, A. 1803. Flora boreali-americana, sistens caracteres plantarum quas in America septentrionali collegit et detexit Andreas Michaux. Apud Fratres Levrault, Paris and Strasbourg, France. NatureServe. 2005. NatureServe Central Databases. Arlington, Virginia. USA New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY. Philbrick, C.T. and A. Novelo R. 2004 Monograph of Podostemum (Podostemaceae). Systematic Botany Monographs 70: 1-106. 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. Sprague, T.A. 1933. Podostemaceae or Podostemonaceae. Bulletin of Miscellaneous Information (Royal Gardens, Kew) 46: 46. Weakley, A. S. 2007. Flora of the Carolinas, Virginia, Georgia, and surrounding areas. Working draft of 11 January 2007. University of North Carolina Herbarium (NCU), North Carolina Botanical Garden, University of North Carolina at Chapel Hill. Online. Av 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/ 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, New York Natural Heritage Program This project is made possible with funding from: 625 Broadway, 5th Floor, - New York State Department of Environmental Conservation Hudson River Albany, NY 12233-4757 Estuary Program Phone: (518) 402-8935 - Division of Lands & Forests, Department of Environmental Conservation [email protected] - New York State Office of Parks, Recreation and Historic Preservation Information for this guide was last updated on Nov 23, 2015 This guide was authored by NYNHP Conservation Guide - Riverweed (Podostemum ceratophyllum) 5