Bucklandiella lusitanica

The diversity of mosses is much higher than many people realise. Whereas some moss species have wide ranges that may cross between continents and hemispheres, others are unique to very specific regions and habitats. Among examples of the latter is the European species Bucklandiella lusitanica.

Illustrations of Bucklandiella lusitanica, from Ochyra & Sérgio (1992). Top left: habit; top right: section of stem of hair-leafed form when dry; lower left: section of stem of hairless form and sporophyte when wet.

Bucklandiella lusitanica was only described as a new species (under the name Racomitrium lusitanicum) in 1992 (Ochyra & Sérgio 1992), having gone unnoticed previously despite being a relatively distinctive species. Recent collections of the species have been identified from a single region, the Serra do Gerês mountain rainge and Parque Natural da Peneda-Gerês national park in the northwest of Portugal, at altitudes between 650 and 1000 metres. A single collection from the Serra do Estrela further south in the country was made in the mid-1800s though it went unidentified at the time. Its rarity is such that is has officially been listed as Endangered by the IUCN. Bucklandiella lusitanica is a rheophyte, which is to say that it grows in association with running water. It grows on acidic granite rocks that are periodically or permanently submerged, such as alongside streams and waterfalls. It is particularly abundant on steep rock faces, growing in association with closely related moss species.

Appearance-wise, Bucklandiella lusitanica is a medium-sized moss with irregularly branched stems growing 1.5 to 3.5 centimetres in length. Leaves are rigid, held tight to stem, and two or three millimetres long.One of the species' most distinctive features is a broad, fleshy margin to each leaf that is generally two or three cells thick whereas the lamina of the leaf is mostly only a single cell thick. The alar cells at the base of the sides of the leaf often form inflated, strongly coloured lobes. The leaves commonly end in a fine, colourless hair-point. The structure of the leaves is similar to that of Bucklandiella lamprocarpa, another aquatic moss species, but that species lacks the hair-points. The two species also differ in the form of their spores, those of B. lamprocarpa being larger and more ornate than those of B. lusitanica, and B. lamprocarpa has fatter and often shinier capsules than B. lusitanica.

I mentioned previously that Bucklandiella lusitanica was originally described as a member of the genus Racomitrium. The moss genus Racomitrium was long recognised by a distinctive array of features including leaf lamina cells with distinctly sinuous longitudinal cell walls, a calyptra (the cap of the developing capsule) that is basally frayed into several lobes, and teeth of the peristome (the teeth around the aperture of a mature capsule) that are split into two or more segments (Sawicki et al. 2015). Racomitrium in this sense was a diverse genus with over two hundred species having been named at one time or another, and somewhere between sixty and eighty species recognised as valid in recent years, As a result, Ochyra et al. (2003) proposed the division of Racomitrium in the broad sense between four separate genera. Bucklandiella, the largest of these segregate genera (with about fifty currently known species), was recognised for species with a smooth leaf surface (lacking papillae on the lamina) and relatively short, shallowly divided teeth in the peristome. The division of Racomitrium has not been universally accepted. Larrain et al. (2013) questioned the monophyly and diagnosability of Ochyra et al.'s segregates but Sawicki et al. (2015) reiterated their support for the new system (and added a fifh new segregate genus to boot). It is generally accepted that Racomitrium in the broad sense represents a monophyletic unit, so the question of whether lusitanicum should be assigned to Racomitrium or Bucklandiella may largely be considered a question of just how closely circumscribed you feel a genus should be.

REFERENCES

Larraín, J., D. Quandt, M. Stech & J. Muñoz. 2013. Lumping or splitting? The case of Racomitrium (Bryophytina: Grimmiaceae). Taxon 62 (6): 1117–1132.

Ochyra, R., & C. Sérgio. 1992. Racomitrium lusitanicum (Musci, Grimmiaceae), a new species from Europe. Fragmenta Floristica et Geobotanica 37 (1): 261–271.

Ochyra, R., J. Żarnowiec & H. Bednarek-Ochyra. 2003. Census Catalogue of Polish Mosses. Institute of Botany, Polish Academy of Sciences: Cracow.

Sawicki, J., M. Szczecińska, H. Bednarek-Ochyra & R. Ochyra. 2015. Mitochondrial phylogenomics supports splitting the traditionally conceived genus Racomitrium (Bryophyta: Grimmiaceae). Nova Hedwigia 100 (3–4): 293–317.