Beach pinweed (Lechea maritima) COSEWIC assessment and status report: chapter 8

Biology

Very few studies exist on the reproductive biology of Cistaceae species and little specific information is available on the biology of Lechea maritima var. subcylindrica or Lechea maritima more broadly. Most information found refers to the plant family or genus in general with that information augmented here by field observations.


Life Cycle and Reproduction

Beach pinweedis a low herbaceous perennial with mostly erect fruiting stems and prostrate basal shoots growing from a woody taproot. The species reproduces by seed, flowers in mid- to late summer, and produces fruit in early fall. Flowers open only for a short time (Hodgdon 1938, Fernald 1950), typically in bright sunshine (Britton 1894). They are reddish-brown, perfect flowers and are borne in panicles (Hodgdon 1938). The stamens first become exerted and pollen is shed once the ovary has grown as long as the sepals and the three red feathery stigmas have become receptive (Barringer 2004). A variety of pollination biology or breeding systems have been documented in Cistaceae taxa, including obligate outbreeding, selfing and cleistogamy (Talavera et al. 1992) and the occurrence of reduced cleistogamous flowers has been reported in Lechea (Herrera 1992, Nandi 1998). Although Lechea maritima has been referred to as being self-fertilized (Kearney 1901), Hodgdon’s (1938) suggestion of frequent hybridization between species would imply outbreeding to some extent. Although the small flowers and red petals could indicate pollination by small Diptera or Lepidoptera species, flower morphology (exerted stamens and feathery stigmas), preference for open habitat and an apparent lack of nectar production suggest wind pollination (Barringer 2004).

Basal shoots appear after flowering in late summer or early fall and their leaves fully develop in fall (Britton 1894). These basal shoots last through the winter then either die back in late spring and summer or shoot up from the tip to form erect fruiting stems (Barringer 2004). Fruiting shoots frequently remain erect through the winter months and into the following spring, which likely allows seed dispersal by wind over snow and ice. Some seeds were found to be remaining on old flowering stalks in mid-February 2007.

There is limited information on longevity in pinweeds, although Hodgdon (1938) did note a greater frequency of biennial plants and occasional production of limited fruit after one growing season toward the northern edge of the range. A few cases of beach pinweed plants producing a limited number of flowers at very small sizes, apparently within two years of germination (C.S. Blaney, pers. obs. at Fox and Hog Islands, 2005) were found. These small plants had only tiny taproots about 1mm wide and no basal shoot development, compared to the thick (>5mm), woody taproots and dense basal rosettes of the more typical larger plants observed. It seems reasonable to assume that these much larger plants are considerably older than two years, and an estimate of 8-10 years is probably a conservative one for generation time (average age of reproductive individuals).


Herbivory

No signs of substantial herbivory were detected during field surveys and no mention of this was found in the pertinent literature. Historically, the sites of certain populations have been used as pasture for livestock and the species could have been subjected to grazing at that time.


Dispersal

As observed in other Cistaceae (e.g., Talavera et al. 1992), seed dispersal in Lechea most likely occurs via the shaking of branches by wind and precipitation. In a study of seed dispersal in Cistus species, seed density in the soil was shown to reach its peak beneath the plant canopy, indicating that seeds are mostly dispersed over very short distances (Bastida and Talavera 2002). According to Thanos et al. (1992), there seems to be no specialized mode of dispersal in Cistaceae species and seeds presumably disperse in the vicinity of the mother plant. Seeds might be carried over greater distances by water or by high winds, especially over ice and snow. The stalks, which often remain erect for a year after flowering, were found to retain some seeds into mid-February. No evidence of animal-mediated dispersal was found in the literature reviewed for this report, though it might occur through wet seeds sand sticking to animal fur, feathers or feet.


Interspecific Interactions

Studies indicate that most Cistaceae form symbiotic relationships with either specific or aspecific root mycobionts (Giovannetti and Fontana 1982, Malloch and Thom 1985, Comandini et al. 2006). In an investigation of North American genera, Malloch and Thorn (1985) confirm that both Lechea and Hudsonia species show evidence of ectomycorrhizae with unidentified fungi. Generally, such relationships are very beneficial to the host plant, facilitating water and nutrient absorption from the soil and increasing resistance to drought and soil-borne pathogens, thus improving the capacity to withstand harsh conditions such as those found in dune habitats. It is unclear whether availability of compatible fungi could limit beach pinweed distribution. An interesting line of speculation in this regard involves the fungus Leccinum arenicola, originally described from coastal dunes in New Brunswick as a presumed mycobiont of beach heather (Hudsonia tomentosa) (Redhead and Watling 1979). If Canadian plants of L. maritima and Hudsonia tomentosa formed mycorrhizal relationships with the same fungus species, it could explain why these two plants frequently occur in association.

Hodgdon’s (1938) field observations and morphological analysis of herbarium specimens suggested that L. maritima can occasionally hybridize with Lechea villosa, L. minor and L. intermedia; however, Hodgdon (1938) and David Lemke (pers. comm.), author of the upcoming Flora of North America treatment for the genus, believe the taxa are all good species. Beach pinweed’s range overlaps only with L. intermedia, which is also found in New Brunswick and Prince Edward Island in a variety of dry and disturbed habitats. Although the two species were seen in fairly close proximity at three sites, no hybrids were detected during field surveys and the species were clearly separable morphologically and ecologically.


Physiology/Adaptability

As with most other Cistaceae, the majority of seeds in a given Lechea maritima seed bank generally have a hard, impermeable coating and only a small fraction are capable of germinating over the short term (Thanos et al. 1992). Seeds can therefore remain dormant for extended periods of time, until the seed is scarified, creating openings in the seed’s surface layer and allowing water absorption and germination. Together with a small seed size which facilitates penetration and accumulation in the soil (Fenner 1985) and opportunistic germination in a wide range of temperature and light conditions (Thanos et al. 1992), this type of primary seed dormancy is part of an adaptive strategy that allows plants to persist in difficult environments and effectively recolonize areas affected by heavy disturbance. Such adaptations make the species well suited to dune habitats that may be subjected to storm overwash and severe drought. Tests have shown that Lechea maritima seeds initially exhibit a low germination rate (6%) but can reach a high germination rate (75%) following abrasion (Thanos et al. 1992).

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