BFNA Title: Pseudoditrichaceae
Author: A. J. Shaw
Date: March 23, 2009
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
BFNA Web site: http://www.mobot.org/plantscience/BFNA/bfnamenu.htm

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Pseudoditrichaceae Steere & Iwatsuki

A. Jonathan Shaw

Plants acrocarpous, scattered or gregarious. Stems short, 1--3 mm, unbranched. Leaves erect-spreading, secund, linear-lanceolate from an oblong ± sheathing base, serrulate to irregularly serrate at the shoulders, costa narrow, delicate proximally, nearly filling the acumen; cells ± thick-walled, in leaf base long-rectangular, longer on costa (distal portion of leaf), irregularly rhombic at the shoulders. Specialized asexual reproduction common, of ± spherical, reddish brown rhizoidal tubers, axillary, filiform to bulbiform gemmae. Sexual condition dioicous; male plants smaller, with less secund leaves than females; perichaetial and perigonial leaves scarcely differentiated. Seta single, reddish brown, delicate, ca. 6 mm. Capsule suberect, ovoid, reddish brown; exothecial elongate-rectangular, thick-walled, with straight or slightly sinuose, thickened walls, slightly collenchymatous; annulus present, revoluble; operculum short-conic; peristome diplolepideous-alternate, exostome pale yellow to hyaline, narrowly lanceolate, somewhat irregular, trabeculate, pitted basally, papillose distally, endostome hyaline to pale yellow, segments divided to base and diverging, halves of adjacent segments converging opposite exostome teeth, basal membrane low, scarcely exceeding the capsule rim, cilia absent. Calyptra fugacious, cucullate, smooth or slightly papillose distally. Spores shed singly, 15--21 \um, papillose.

Genus 1 (species 1): Arctic North America.

Selected references. Steere, W. C. and Z. Iwatsuki. 1974. Pseudoditrichum mirabile gen. et. sp. nov. (Musci: Pseudoditrichaceae fam. nov.), a unique moss from Great Bear Lake, Northwest Territories. Can. J. Botany 52: 701--706. Shaw, A. J. 1984. A reinterpretation of peristome structure in Pseudoditrichum mirabile Steere and Iwatsuki (Pseudoditrichaceae). Bryologist 87: 314--318.

The family Pseudoditrichaceae consists of one genus and one species, known only from the type specimen collected near Great Bear Lake, Northwest Territories. In the original description, W. C. Steere and Z. Iwatsuki (1974) interpreted the endostome segments as opposite the exostome teeth. A. J. Shaw (1984) showed that the “opposite” segments consist of two halves of adjacent alternate segments that are split to and diverge from their bases, and that the peristome should be interpreted as diplolepideous-alternate. The gametophytes are scarcely distinguishable from those of Ditrichum. This and the unique peristome warrant familial recognition.

1. Pseudoditrichum Steere & Iwatsuki, Can. J. Bot. 52. 701. 1974 * [Alluding to the gametophyte morphology similar to that of Ditrichum]

Plants very small. Leaves narrowly lanceolate from an ovate to oblong base, erect-spreading, ± secund. Capsule exostome teeth lanceolate, ± irregular; endostome segments split to the base, divergent and appearing opposite, basal membrane nearly absent.

Species 1, Arctic North America.

1. Pseudoditrichum mirabile Steere & Iwatsuki, Can. J. Bot. 52. 701. 1974

Plants tiny. Capsule suberect, ovoid.

Capsules mature summer (July). Moist calcareous silt, under Populus; N.W.T.

Pseudoditrichum mirable was collected in 1948 but not described until 1974. The gametophytes look like a very small Ditrichum, but the peristome is definitely diplolepideous (and therefore this taxon is not related to Ditrichum). It has not been recollected since its discovery. Great Bear Lake is an unlikely place to find the only population of an endemic species, genus, and family, but the plants have a unique combination of gametophyte and sporophyte features that do not fit into any other family.