Beach pinweed (Lechea maritima) COSEWIC assessment and status report: chapter 5

COSEWIC Status Report
on the
Beach Pinweed
Lechea maritima
in Canada
2008

Species Information

Name and Classification

Scientific name:
Lechea maritima Leggett
Synonyms:
Lechea maritima Leggett var. subcylindrica Hodgdon
Species-level synonymy:
Lechea thymifolia Pursh
Lechea minor L. var. maritima A. Gray
English vernacular names:
Beach pinweed, Gulf of St. Lawrence beach pinweed, maritime pinweed, hoary pinweed, seaside pinweed
French vernacular names:
Léchéa du Golfe Saint-Laurent, Léchéa maritime, Léchéa de la mer
Family:
Cistaceae, rock-rose family
Major plant group:
Eudicot flowering plant

Beach pinweed (Lechea maritima) is a member of the Cistaceae, a medium-sized family of about 200 species in nine genera. The family is composed of mesophytic and xerophytic herbs, shrubs and sub-shrubs, and reaches its highest concentrations of species in arid Mediterranean regions of the Iberian Peninsula and the Atlantic Coastal Plain of North America (Hodgdon 1938).

The genus Lechea L., containing 17 species (Hodgdon 1938), is restricted to the United States, Canada and northern Mexico, with the exception of one species endemic to western Cuba and two species present in southern Mexico, Belize and Guatemala. Commonly referred to as pinweeds, the species in this genus are typically perennial or biennial herbs found growing on dry sandy or rocky substrates in open and exposed habitats. Their diversity is highest on the Atlantic Coastal Plain. The genus was named by Kalm in 1751 in honor of John Leche, a Swedish botanist, and was taken up by Linnaeus in 1753 in the first edition of Species Plantarum (Britton 1894). As was summarized by Hodgdon (1938), it subsequently underwent several revisions in the 19th century, but variability and the often microscopic diagnostic characters led to great variations between the early treatments. The most recent and complete revision is that of Hodgdon (1938), which established the species concepts in use today.

Despite a somewhat confusing taxonomic history outlined below, beach pinweed (Lechea maritima) is considered distinct from all other Canadian Lechea species (David Lemke, author of Lechea account for Flora of North America, pers. comm.). The Gulf of St. Lawrence variety of beach pinweed (Lechea maritima var. subcylindrica) is the only variety definitively known for Canada, with reports of Lechea maritima var. maritima from Quebec and Ontario apparently erroneous, as outlined under Canadian Range below. Thus, although the distinctness of var. subcylindrica may warrant further taxonomic enquiry, at the species level Lechea maritima is definitely a valid unit for COSEWIC status evaluation.

Lechea maritima Leggett was first included within L. thymifolia Pursh in 1814. Lechea maritima has at times also been included under L. thymifolia Michaux, a name that is properly synonymized with the present L. minor L. (Hodgdon 1938). Gray’s work in 1890 referred to L. maritima as L. minor L. var. maritima A. Gray. Britton’s revision of the genus in 1894 established the name L. maritima Leggett for L. thymifolia Pursh. Hodgdon (1938) described marked variants of the species, including var. subcylindrica, on the basis of differences in panicle shape and branching, sepal characters and seed number, with the type specimen of var. subcylindrica having been collected by S.F. Blake in 1913 on Portage Island, New Brunswick, and located at the Gray Herbarium. Hodgdon specifically identified all the Canadian records known at that time, from five New Brunswick sites, as variety subcylindrica. The distinctness of Lechea maritima var. subcylindrica Hodgdon has not been specifically investigated since that time, but the variety was retained by Fernald (1950) and Kartesz (1999) and was noted as “segregated on minor differences” in Gleason and Cronquist (1991). Hodgdon (1938) examined no specimens from Prince Edward Island, but specimens collected there in recent years key to var. subcylindrica (Catling et al. 1985, D.M. Mazerolle & C.S. Blaney, pers. obs.), with some variation in inflorescence shape.


Morphological Description

The following description has been derived from Hodgdon (1938), Barringer (2004), Fernald (1950), Gleason and Cronquist (1991) and Britton (1894). Figure 1 illustrates the plant in the field.

The following description is based on Lechea maritima var. subcylindrica. Beach Pinweed is a low, herbaceous perennial arising from a woody taproot up to 10 cm long. The fruiting stems are (10) 20-35 cm long, reclining to erect and strongly branched. Prostrate to reclining basal shoots 3-10 cm long develop from the woody base, often forming a rosette. The crowded basal leaves are whorled, thick, dull green, lanceolate to elliptic-lanceolate, 5-12 mm long, 2-5 mm wide, minutely pilose above and densely white pilose below. The stem leaves are narrowly elliptic to narrowly oblanceolate, 7-25 mm long, 1.2-4 mm broad. They are scattered-pilose over the lower surface with a smooth to scattered-pilose upper surface becoming glabrous in maturity. Stem leaves are opposite or whorled, with the lowermost sometimes subopposite. Leaves on branches are alternate, often crowded and mostly persistent and are shorter and proportionately narrower. The inflorescence is a narrowly subcylindric panicle, as referenced by the varietal name, with branching beginning mostly above the middle of the stem. Numerous inconspicuous flowers are crowded in small axillary or terminal clusters of 3-6 or are arranged in racemes on short tertiary branches borne towards the secondary branch tips. Flowers are 2-4 mm broad and perfect with a superior ovary. The 3 petals are short-lived, reddish-brown and generally shorter than the sepals. Flower structures are regular except for the slightly depressed-globose persistent calyx (2 mm or slightly more in length), which is of 5 sepals in two distinct series. The inner 3 sepals are thin and membranous, obscurely keeled, pubescent, ovate-elliptic and subacute while the outer 2 are leaf-like, narrowly lanceolate to linear and shorter than or equal to the inner. Number of stamens varies, even among flowers on the same plant, from 6 to 10 or more. There are 3 fringed-plumose stigmas, either sessile or on a very short style. The fruit is an ovoid or globose 3-valved capsule (1.8-2.1 mm long) usually shorter than the calyx, splitting open lengthwise to the base. The (3)4-5(6) seeds per capsule are 1-1.1 mm long, dull light brown in color, smooth and nearly equilateral with a convex dorsal surface and a convex or keeled ventral surface. They lack a membranous cover and a slender straight or curved embryo is faintly discernible through the semitransparent endosperm.


Figure 1: Beach pinweed (Lechea maritima) with two flowering stems and basal rosette

Beach pinweed (Lechea maritima)

Beach pea (Lathyrus japonicus) and American beachgrass (Ammophila breviligulata) are in the right foreground.

Excerpted from Hodgdon’s (1938) analysis of Lechea maritima, the following key distinguishes var. subcylindrica from var. maritima. An additional variety, var. virginica, occurs in coastal southern Virginia and northern North Carolina and has been confirmed as distinct in a recent study (Sorrie and Weakley 2007).

Panicles thick-subcylindric to broadly subpyramidal, and mostly uniformly branching at about the middle of the stems. Calyx mostly pyriform to obconic or subglobose (cuneate-obovoid), 2 mm or less in length. Outer sepals inconspicuous and much shorter than the inner. Seeds 3-4 (rarely 5). Ranging from Maine to Maryland. var. maritima

var. maritima

Panicles slenderly subcylindric, their branches mostly from above the middle of stem. Calyx slightly depressed-globose, 2 mm or slightly more in length. Outer sepals often conspicuous and sometimes nearly equaling the inner. Seeds 4-5(6). Restricted to Gulf of St. Lawrence coasts of New Brunswick and Prince Edward Island. var. subcylindrica

var. subcylindrica

Mature specimens with basal shoots and use of a hand lens may be necessary for positive identification of many Lechea species. The Canadian populations of beach pinweed are geographically isolated from other L. maritima varieties in the U.S. and are sympatric only with narrowleaf pinweed (Lechea intermedia), a more common and less habitat-specific species. In Canada, Lechea maritima and L. intermedia can occur in close proximity and are best distinguished by basal leaf pilosity and seed texture. In L. intermedia, mature seeds are conspicuously reticulate, and pubescence on the undersurface of basal leaves is restricted to the midribs and margins. In L. maritima var. subcylindrica seeds are smooth and basal leaves are pubescent over the entire undersurface.


Genetic Description

David Lemke, author of the Flora of North America treatment for Lechea, is unaware of any chromosome counts or other genetic analysis of Lechea maritima or any other Lechea species (Lemke 2007, pers. comm. to Sean Blaney).


Designatable Units

Only a single designatable unit is recognized since all of the populations occur within relatively restricted shoreline stretches within a single COSEWIC National Ecological Area (Atlantic) that encompasses the species’ range in New Brunswick and Prince Edward Island.

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