Alnus maritima 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Fagales Betulaceae

Scientific Name: Alnus maritima (Marshall) Muhl. ex Nutt.
Common Name(s):
English Seaside Alder, Brook Alder
Betula-alnus maritima Marshall
Taxonomic Notes: Furlow (1979) published, “The systematics of the American species of Alnus (Betulaceae)" in Rhodora.  Furlow 1997 followed the taxonomy presented in his 1979 paper in his treatment of Alnus in the Flora of North America recognizing Alnus maritima as a taxon with no infraspecific taxa recognized.  Schrader and Grove (2002, 2004) made the case for recognizing three disjunct populations of A. maritima as three separate taxa; A. maritima subsp. maritima (Delmarva Peninsula, Delaware and Maryland); A. maritima subsp. georgiensis Schrader & Graves (Bartow County, Georgia); and, A. maritima subsp. oklahomensis Schrader & Graves (south-central Oklahoma).  Gibson et al. (2008) compared the genetic diversity of the three disjunct populations of A. maritima against the genetic diversity of A. serrulata.  Their findings and conclusions were consistent with the genetic work of Schrader and Graves (2004). Research using microsatellites (Jones and Gibson 2011, Jones, 2013) supported the previous taxonomic conclusions that A. maritima is composed of three geographically disjunct subspecies, subsp. maritima, subsp. georgiensis, and subsp. oklahomensis. NatureServe (2013) last reviewed the conservation status of A. maritima in 2011. NatureServe recognizes all three subspecies of A. maritima; subspecies maritima, georgiensis, and oklahomensis.

Assessment Information [top]

Red List Category & Criteria: Endangered B2ab(ii,iii,iv) ver 3.1
Year Published: 2016
Date Assessed: 2014-08-01
Assessor(s): Stritch, L., Roy, S., Shaw, K., Wilson, B. & Rivers, M.C.
Reviewer(s): Oldfield, S.

Endemic to the United States, Alnus maritima is a disjunctly distributed tree species, with subpopulations so widely separated that they are considered distinct subspecies. The distinct genetic identity of each subspecies, the reduced genetic diversity within each subspecies and the lack of gene flow among subpopulations within each region means that it is important to protect plants at all sites to conserve the genetic diversity and long-term viability of the species.

The combined area of occupancy of the fragmented subpopulations is estimated to be 394 km2 (using a 2x2 km2 grid, although the area occupied is much smaller as the species is distributed linearly along streams and riverbanks). A combination of threats impact upon the Alnus maritima complex, including climate change, grazing and low genetic diversity, which are projected to cause decline in area of occupancy, extent, area and quality of habitat and number of subpopulations. This species is assessed here as Endangered.

Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is endemic to the USA. It is found growing at low altitudes (0 to 100 m asl) in Delaware (subsp. maritima), Georgia (subsp.  georgiensis) Maryland (subsp. maritima) and southern Oklahoma (subsp. oklahomensis). It is a disjunctly distributed tree species, with populations so widely separated that they are considered distinct subspecies. The extent of occurrence is large (400,000 km2) due to its widely separated subspecies, however, the combined area of occupancy is estimated to be less than 500 km2, meeting the threshold for consideration as Endangered. The area of occupancy for subsp. georgiensis is estimated to 0.14 km2, however, using a 2x2 km grid this would be 4 km2. Similarly the area of occupancy of subsp. oklahomensis is estimated to 2.97 km2 due to its linear habitat (along streams), however using a 2x2 km2 grid on this habitat the area of occupancy is estimated to be 190 km2. Finally for the subsp. maritima, the area of occupancy is more difficult to estimate, but is likely to be less than 200 km2. Therefore the collective area of occupancy is less than 394 km2.
Countries occurrence:
United States (Delaware, Georgia, Maryland, Oklahoma)
Additional data:
Estimated area of occupancy (AOO) - km2:394Continuing decline in area of occupancy (AOO):Yes
Estimated extent of occurrence (EOO) - km2:400000
Upper elevation limit (metres):100
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The subpopulations of Alnus maritima probably represent remnants of a more widespread Pleistocene and post-Pleistocene distribution. This species is locally frequent along the Nanticoke River (Delaware and Maryland), and is known from a few other rivers and creeks nearby on the Delmarva Peninsula. This species is also known from two highly disjunct areas: two nearby perennial streams in the cross-timbers region of southern Oklahoma, and one population in Georgia.

Each subspecies has distinct genetic identity with a lack of gene flow among populations.  Subpopulations of Seaside Alder appear stable in both Delaware (William McAvoy, Delaware Dept. of Natural Resources and Environment, pers. comm.) and Maryland (Chris Frye, Maryland Dept. of Natural Resources, pers. comm.). The other two subpopulations are also recorded as stable.


Current Population Trend:Stable
Additional data:
Population severely fragmented:Yes
Continuing decline in subpopulations:Yes

Habitat and Ecology [top]

Habitat and Ecology:This species is a large shrub or small deciduous tree occurring along edges of ponds and small streams, often in standing water. As with all other species of Alnus, it can fix nitrogen. Seaside Alder (subsp. maritima) only occurs in fresh water tidal and non-tidal systems (William McVoy, Delaware Dept. of Natural Resources and Environment, pers. comm.). Seaside Alder occurs in open sunny areas and not in shaded occasions (Schrader et al. 2006, Rice and Gibson 2009). Oklahoma Alder occurs along fast moving rivers and creeks in Oklahoma.  Oklahoma Alder occurs in shallow water at the edges of two rivers where it occurs. In all instances Oklahoma Alder occurs in open sunny areas and not in shaded occasions (Schrader et al. 2006, Rice and Gibson 2009).

Systems:Terrestrial; Freshwater
Continuing decline in area, extent and/or quality of habitat:Yes

Use and Trade [top]

Use and Trade: There is no use or trade information available for this species; has potential to be used as a biomass crop

Threats [top]

Major Threat(s): A combination of threats impact upon the Alnus maritima complex, including climate change, grazing (run-off) and low genetic diversity (Jones and Gibson 2011), which are projected to cause decline in extent of occurrence, area of occupancy, quality of habitat and number of subpopulations. As sea levels  rise due to climate change, salt water intrusions into the current fresh water tidal systems will threaten populations of seaside alder  (William McVoy, Delaware Dept. of Natural Resources and Environment, pers. comm.).  

Conservation Actions [top]

Conservation Actions: Ex situ collections exist for some subspecies, and parts of the distribution is within protected areas. Increased conservation measures, in situ and ex situ, are recommended. This species has a NatureServe ranking of Vulnerable. The reasons for this are its scattered range (small areas of Oklahoma, southwestern Delaware and adjacent eastern Maryland, and one areas in Georgia), with few sites overall. This species was listed as Rare in Delaware and Maryland, and Vulnerable in Oklahoma in the 1997 IUCN Red List of Threatened Plants and LR/nt in the World List of Threatened Trees in 1998.

For  Alnus maritima subsp. maritima, there are currently no active conversation actions except for qualitative monitoring.  The most practicable conservation measure to implement is ex situ conservation, seed collection, of Seaside Alder throughout its range in the Delmarva Peninsula.

For  Alnus maritima subsp. georgiensis three experimental research populations have recently been established on protected lands to study the ability to establish additional populations. Ex situ collections have been established at the Atlanta Botanical Garden and the State Botanical Garden of Georgia.  Ex situ seed collections have also been made (J. Mincy Moffett, Georgia Department of Natural Resources, pers. comm. 2013).

For  Alnus maritima subsp. oklahomensis, the state of Oklahoma has a wildlife management area along the Blue River that contains a number of Oklahoma alders.  The Nature Conservancy has also bought property along the Blue River. Conservation easements are being pursued to protect populations on both the Blue River and Pennington Creek. A graduate student is conducting research on the establishment of Oklahoma Alder on an island in the Blue River to determine if out-planting is a viable conservation action.

Citation: Stritch, L., Roy, S., Shaw, K., Wilson, B. & Rivers, M.C. 2016. Alnus maritima. The IUCN Red List of Threatened Species 2016: e.T34053A2841625. . Downloaded on 19 September 2017.
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