Porsild's bryum (Haplodontium macrocarpum) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

There is no officially recognized common name for this moss species in either English or French. Recent DNA sequencing data and phylogenetic analyses have shown Mielichhoferia macrocarpa (Hook.) Bruch & Schimp. belongs in the genus Bryum (Cox et al. 2000). Mielichhoferia macrocarpa resolves in a clade with members of section Bryum, and a new name, Bryum porsildii (I. Hagen) Cox & Hedderson, has been submitted for publication in the Journal of Bryology (C. Cox and T. Hedderson, pers. comm.). Hedderson and Cox have provided the following protologue:

Bryum porsildii (I. Hagen) Cox & Hedderson, nov. comb.

Basionym:   MielichhoferiaporsildiiI. Hagen, Meddelelser om Grønland 26: 437. 1904

Synonyms: Weissia macrocarpa W. J. Hooker ex Drummond, Musci Americani, Specimens of the Mosses Collected in British North America 74. 1828, non Bryum macrocarpum Hedwig, Species Muscorum 178. 1801, nec Withering, Systematic Arrangement of British Plants ed. 4, 3: 805. 1801, hom. illeg., nec (Hoppe & Hornschuch) Bridel, Bryologia Universalis 1: 648. 1826, hom. illeg., nec R.Br.ter, Transactions of the New Zealand Institute 31: 455. 1899, hom. illeg.; Mielichhoferia macrocarpa (W.J. Hooker ex Drummond) Bruch & W. P. Schimper, London Journal of Botany 2: 665. 1843; Mielichhoferia nitida var. macrocarpa (W.J. Hooker ex Drummond) Müller Hal., Synopsis Muscorum Frondosorum 1: 235. 1848. Mielichhoferia nitida var. gymnostoma Mitten ex W. J. Hooker, Journal of the Linnean Society, Botany 1:119 .1857. Bryum nelsonii Kindberg, Revue Bryologique 36: 98. 1909. Mielichhoferia macrocarpa var. pungensE.B. Bartram, Bulletin of the Torrey Botanical Club 54: 33. 1927.

Description

Mielichhoferia macrocarpa plants are relatively small (0.3 to 1.0 cm high) and grow tightly together such that their much branched stems form short, compact cushions (Figure 1). These cushions are bright green and have a "spongy texture" as noted by Flowers (1973). Individual stems are reddish brown and branch by innovations (Figure 2 a,b). The older portions of the stems are covered in dense red rhizoids and often the leaves have lost their chlorophyll and appear colorless except for the costa, which becomes red with age. The leaves are somewhat concave and recurved and appear shiny due to the lax thin-walled cells (Figure 2 c,d). The leaves vary between 0.6 and 1.5 mm long. The species is dioicous, that is, there are separate male and female (gametophytic) plants. The male gametophytes are smaller than the females and have a more rosette-like arrangement of crowded concave leaves at the stem apex (Figure 2a). The female plants are larger and have longer leaves that are less concave and more evenly spaced on the stems (Figure 2b). Cushions of female plants often produce copious sporophytes and the setae of the sporophytes are largely hidden by the newest stem innovations (Figure 3). The capsules (sporangia) are somewhat globose because they round to a relatively narrow mouth. The species is fairly distinct and uniform in North America, although the populations seen from Colorado differed in their relatively larger plants having long, almost linear leaves with frequently excurrent costae.

Figure 1. Closeup of Mmac1 population in Mountain Park, Alberta showing the deep, spongy cushions of Mielichhoferia macrocarpa.

Figure 1. Closeup of Mmac1 population in Mountain Park, Albertashowing the deep, spongy cushions of Mielichhoferia macrocarpa

 

Figure 2. Mielichhoferia macrocarpadetails drawn from plants of the Whitehorse Creek Rapids population.

  1. male plant.
  2. female plant.
  3. older leaf taken from base of the sporophyte. Note the recurved margins and loss of color in all but the costa.
  4. younger leaf from shiny green new growth of stem. Note lax leaf cells and plane, entire margins with longer thinner cells.

Scale bar: 0.4 cm for a and band 0.6 mm for c and d.

Figure 2.  Mielichhoferia macrocarpa details drawn from plants of the Whitehorse Creek Rapids population. a male plant.b female plant. c older leaf taken from base of the sporophyte. Note the recurved margins and loss of color in all but the costa. d younger leaf from shiny green new growth of stem. Note lax leaf cells and plane, entire margins with longer thinner cells. Scale bar: 0.4 cm for a and b and 0.6 mm for c and d.

 

Figure 3. Closeup photograph of a Mielichhoferia macrocarpa colony growing along Whitehorse Creek with copious sporophytes and the setae largely hidden by the new stem growth of the colony.

Figure 3. Closeup photograph of a Mielichhoferia macrocarpa colony growing along Whitehorse Creek with copious sporophytes and the setae largely hidden by the new stem growth of the colony.

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