re-evaluation of tortella - Missouri Botanical Garden

agree about this species." He put T. nitida in the genus
Trichostomum in the basis of the presence of a stem
central strand.
The type specimen of Tortella nitida strongly
resembles the autoicous Tortella humilis except for the
massive costa, in section with two well-developed
stereid bands. It is perhaps because of this that
Limpricht (1890) wondered whether T. nitida might
possess axillary male buds. Tortella nitida differs from
T. humilis immediately by its long stem and elongate
habit, rather than the typically much shorter stem and
rosulate habit of T. humilis. The cross section of T.
humilis in the middle of the leaf is adaxially flat.
Although the type of T. nitida has leaves that appear
adaxially flat, most specimens are more tubulose, with
margins erect and broadly incurved. Although both
species have gradually intergrading proximal cells,
those of T. nitida are more strongly intergrading: the
marginal cells in the proximal area are more
conspicuously set off as a border of lax-walled,
elongate, hyaline epapillose cells, in some specimens so
reduced as to cast doubt that the specimen is a Tortella
at all. Tortella nitida rarely fruits and has short, erect
peristome teeth, whereas T. humilis, at least in North
America, is rarely found without fruit, and its peristome
teeth are long and in one or two spirals.
Tortella nitida has a distinctive growth-form:
in hemispherical cushions, rather like some Grimmia
species, and is frequently represented in herbarium
specimens as fan-shaped slices from the original polster.
None of the species of Tortella that occur in North
America assume this shape except T. inclinata var.
densa.
Tortella nitida has frequently been described as
having a "white" or "pale" costa. Its costa seems,
however, to be in color no different than others in the
genus, except that the costa itself is more prominent
than in other species, especially when the laminae are
folded together when dry and the whole clump of leaves
present their broad backs to view. This whiteness or
paleness apparently is in reference to the "gloss" due to
the smoothness of the costal abaxial surface. The costae
of all species in the genus are yellow or yellow-brown
to orange.
The leaf cross section in highly colored
specimens of Tortella nitida shows a palisade of
quadrate papillose cells on the adaxial surface of the
costa forming a green layer over the orange costa,
confluent with the green color of both laminae. The 1-3
bistratose pairs of guide cells, or incompletely bistratose
guide cell layer, is characteristic of Pseudosymblepharis
and some species of Trichostomum (Zander 1993).
Specimens from Europe show Tortella nitida
to give little indication of its placement in Tortella
except for a narrow border of about two to several cells
width of elongate, thin-walled, smooth hyaline cells,
otherwise the proximal cells are all thick-walled,
colored and gradually become differentiated from the
distal laminal cells. Sometimes the hyaline border is
46
wider and distinct, resembling that of Plerurochaete
squarrosa (Brid.) Lindb.
The fragility of the leaf of Tortella nitida often
expresses itself in moderately scalloped or lobed
margins, with indentations at points of laminal fragility.
The leaves fragment in rectangular units and along the
length of the costa such that in many older leaves the
stem is invested with naked costae divested of the
laminae.
None of the common ovate-lanceolate-leaved
Trichostomum species have fragile leaves.
Trichostomum tenuirostre, in North Temperate stations,
may have fragile, tattered generally long-linear leaves
with a sprawling, loosely tufted habit, occurring with or
without a stem central strand. Tortella alpicola is
similarly fragile and is separated by its diminutive size,
large leaf cells and propagulum at the leaf tip. It is this
fragility that helps to distinguish ambiguous specimens
of Tortella nitida from Trichostomum brachydontium or
Tr. crispulum, since some specimens of the latter
species may show a tendency toward more delicate cells
on the margins of an otherwise intergrading proximal
cell region.
Although most regional floras do not mention
it, neither Trichostomum crispulum nor Tr.
brachydontium are tomentose except at the base, and in
this characteristic Tortella nitida is similar.
William Mitten's isotype (NY) of
Trichostomum diffractum Mitt., now included in the
synonymy of Tortella nitida, was also examined and,
although representing rather smaller plants with
narrower leaves, perhaps characteristic of immaturity, it
matches Lindberg's type. Other collections made by
Mitten in Britain also closely resemble the Lindberg
type.
The description and illustration of fruiting
material here is taken from a single specimen:
Dalmatian plants collected by Jul. Baumgartner 16/III
1904 (S). Clearly the description and illustration of the
peristome of this specimen in the present manuscript
does not match what is described by the following
sources: "peristome teeth short, rather imperfect, very
slightly oblique" (Dixon 1924); "peristome short, of
rather imperfect, very slightly oblique, yellowish,
papillose teeth" (Haring 1938); "Teeth of the peristome
very short and irregular, truncate, yellow, papillose"
(Braithwaite 1887). Mönkemeyer (1927) also indicated
that the peristome of Tortella nitida was rudimentary.
Limpricht (1890), in addition, reported that the cells of
the operculum were straight, the peristome was
rudimentary, yellow-red and smooth, although Philibert
described the teeth as papillose, the basal tube scarcely
or not at all exserted, the teeth linear, scarcely
developed, the longest to 0.07 mm. He appears to have
seen a fruiting specimen, although the species
apparently did not fruit in Germany, Austria or
Switzerland.
The peristome teeth in Braithwaite's illustration
(1887: pl. 37 and reproduced by Haring in Grout 1938:
169, pl. 81) are very short with respect to the capsule