Twisted oak moss (Syntrichia laevipila) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific Name:
Syntrichia laevipila Brid.
Pertinent Synonyms:
Tortula laevipila (Brid.) Schwaegr.
Common Name:
Twisted oak moss
Family:
Pottiaceae
Major Plant Group:
Mosses (Musci)

The Pottiaceae is a large and diverse family of mosses with many of its species restricted to dry environments. It is a taxonomically difficult family and has been undergoing extensive review in recent times (Zander 1993), including the placement of a number of species of Tortula into the genus Syntrichia. The genus Syntrichia is characterized by generally coarse plants, with, usually, entire, awned (with hair-tips) leaves that are ligulate to spathulate and twisted when dry. The sporophytes (spore-producing structures) of Syntrichia have long stems, long-cylindrical, often curved capsules (spore sacs), and well developed, tall peristomes (fringes of tooth-like appendages surrounding the mouth of the capsule), often with basal membranes (Zander 1993; this document provides the rationale for separating Syntrichia from the previously polyphyletic genus Tortula). Closely related species in this genus are often difficult to separate, due to inherent environmental variability and rather subtle morphological differences.

There are ten species of Syntrichia in Canada (Irelandet al. 1987; listed there as species of Tortula). Of these, eight are found in British Columbia, and only one, S. princeps (de Not.) Mitt., is commonly found in similar habitats as S. laevipila, although S. ruralis appears to be present occasionally (W. B. Schofield pers. comm., 2002).

Syntrichia laevipila has two varieties:

  1. var. laevipila, distinguished by leaves with distinct awns and lacking gemmae (asexual reproductive structures), and
  2. var. meridionalis, distinguished by many leaves lacking well developed awns and with copious gemmae in the upper stem axils; its leaves are often eroded and appear to be in poor condition as compared with leaves of var. laevipila.

According to Merrifield (2000), the two varieties often grow together in Oregon, although separate populations of each variety also appear to be common. In a few of the British Columbia populations, intermediate plants are present. It is T. McIntosh’s opinion, based on the examination of numerous collections and supported with information from Merrifield (2000) that a varietal status for either form is unwarranted; Syntrichia laevipila var. meridionalis appears to be a form of S. laevipila characteristic of more stressful habitats, as indicated by the eroded leaves, and, sometimes, more exposed microhabitat. During her extensive survey of S. laevipila on Garry oaks (Quercusgarryana Dougl. ex Hook.) in Oregon, Merrifield (2000) noted that heavy grazing occurs on bryophytes in many localities, probably by insects and, possibly, slugs. She found that the occurrence of S. laevipila var. meridionalis often coincided with heavy grazing, although not always. W. Miles (pers. comm., 2000) found that an unidentified caterpillar chewed a number of stems in one of her collections of S. princeps.

In British Columbia, Syntrichia laevipila var. laevipila can be confused with small plants of S. princeps (larger plants, that is > 1 cm, are readily identifiable as S. princeps). With care, the two species can be distinguished by the following characters:

  1. Leaf size and shape; rarely does S. princeps have leaves as small as var. laevipila, and the leaves of var. laevipila are usually more constricted in mid-leaf,
  2. Leaf margin characters; the leaves of S. princeps are more recurved towards the base,
  3. Sexuality; S. princeps is often synoicous, with both male and female structures found in a single unit, whereas S. laevipila is autoicous, with male units appearing on minute branches along the upper stems below the female structures, and
  4. Number of cell layers above the guide cells (large central cells) of the costa (mid-rib); S. princeps usually has two layers of cells, compared to S. laevipila which has one to, rarely, two layers (Lawton 1971, Kramer 1980).

Confusion with Syntrichia ruralis may also be a problem, but this species was not encountered in this study. The more squarrose (bent away from the stem) leaves of S. ruralis, when wet, as well as its generally more highly recurved leaf margins separate small specimens of this species from S. laevipila.

Worldwide, the taxonomy of this species is complex, especially with respect to the closely related species, Syntrichia pagorum Milde (Crum & Anderson 1981).

Description

The following description has been derived principally from Steere (1939) and Lawton (1971), and from personal observations.

Syntrichia laevipila is an acrocarpous (producing female structures and sporophytes at the tips of the main stems) moss that grows as small clumps on exposed tree bark. It is most readily distinguished by the habitat as well as its diminutive size: it is one of the smallest species in the genus, with stems usually well under 0.5 cm tall. Its oblong to spathulate leaves are twisted when dry, and spreading and slightly recurved when wet. Lawton (1971) notes that they range from 2-3.5 mm in length, but leaves from Canadian populations are rarely over 2 mm long. Leaf margins are often somewhat recurved in the middle of the leaf, but otherwise plane. The leaf mid-ribs are excurrent as smooth to toothed, hyaline awns in var. laevipila (Fig. 1). The awns are very short to absent in var. meridionalis, which is further characterized by the presence of small, generally 0.4 mm long, leaf-like and costate gemmae in the upper leaf axils (Fig. 2). The median and upper leaf cells of S. laevipila are isodiametric to short-rectangular, covered by small papillae (surficial bumps), and range in diameter from 10-16 µm. In some specimens from the United States, the leaves are distinctly bordered by a few rows of thick-walled cells (none of the collections examined for this report had this feature). The basal leaf cells are elongate, smooth, and clear.

Figure 1.  A leaf of Syntrichia laevipila var. laevipila (W. Miles 2002).

Figure 1.  A leaf of Syntrichia laevipila var. laevipila (W. Miles 2002).

Figure 2. A grouping of plants of Syntrichia laevipila var. meridionalis showing gemmae and eroded leaves (W. Miles 2002).

Figure 2. A grouping of plants of Syntrichia laevipila var. meridionalis showing gemmae and eroded leaves (W. Miles 2002).

Syntrichia laevipila is autoicous where both male and female sex organs are found on the same plant. The perigonia, which contain antheridia or the male sex organs, are on short stems below the perichaetia, which contain the female sex organs, the archegonia. The perigonial bracts are small and ovate, with their tips usually bent away from the stem. The cylindrical capsules of S. laevipila are long-exserted, and straight to slightly curved.  Its peristome is long and twisted with a distinct basal membrane. Its spores are papillose and range in size from 9-16 µm.

Taxonomic keys and additional illustrations are found in Steere (1939), Savicz-Ljubitzkaja & Smirnova (1970; in Russian, keys only as illustration appears to be of S. pagorum), Lawton (1971), and Smith (1989).

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