re-evaluation of tortella - Missouri Botanical Garden

inclinata var. inclinata from the three species just
named. Specimens with an adaxial groove of elongate,
smooth cells on the surface of the costa throughout the
leaf and with leaves that are not cucullate but only acute
with a short mucro, may be T. inclinata var. densa
instead. Thickened abaxial and adaxial superficial cell
walls seen in lamina cross-section will also indicate that
variety.
No small, terminal propaguliferous shoots, as
mentioned for English plants of Tortella inclinata var.
inclinata by Smith (1978), were observed or recognized
in North American material. Any terminal filaments
proved to be associated with archegonia, and comprised
the distinctive setaceous apices of perichaetial leaves.
Lack of such shoots in American material may indicate
that European plants could be a somewhat different
taxon. Nyholm (1989) for example, stated that in
Scandinavia: "Short fragile yellow-green apical shoots
are characteristic for this species." Nyholm indicated
that such shoots are important in differentiating the
species from T. densa and T. rigens. It is possible that
these shoots are simply elongations of the main stem
axis and are no more deciduous than the whorls of the
var. densa which disarticulate readily upon dissection.
Tortella inclinata s.l. has up to the present been
the only taxon of the genus in North America to have no
epidermal layer on the costa anywhere on the leaf. Only
the narrow, elongated, smooth stereid cells are exposed
on both surfaces of the costa. In Europe, this species
shares this characteristic with T. rigens, T. densa and T.
limosella (Stirt.) Rich. & Wall. (Smith 1978). Tortella
limosella is separated from T. inclinata in the British
flora in part by having distal leaf cells 8–12 µm wide,
whereas cells of the latter species are 8–10 µm. North
American T. inclinata var. inclinata regularly attains the
larger cell dimensions, however. In addition to larger
cells, T. limosella has thicker cell walls and these are
unipapillose. It was collected once (1906) from dense
patches from a single population on the seacoast in
western Scotland (Smith 1978) and maybe synonymous
with a more inclusive concept of the variability of T.
inclinata s.l.
Persson and Weber (1958), when they first
reported Tortella inclinata from North America,
expressed doubts that the previously described North
American Barbula inclinatula C. M. & Kindb. was
distinct from it. Dixon (1924) reported a different
ecological and distributional regime for European T.
inclinata: "calcareous banks and rocks, usually in
mountainous districts." North American material, for
example, never grows on rocks, but T. inclinata var.
densa does.
Crundwell and Nyholm (1962) stated that the
Müller and Kindberg type of Tortella inclinatula was
identical with European T. inclinata as were two
additonal specimens, one from Ontario and from British
Columbia. Steere and Scotter (1978) still, however,
expressed some hesitation based on a sense that the
perichaetial leaves of the type of Barbula inclinatula
were different from European material. "Macoun's 190
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in the National Museum of Canada (CANM) has
perichaetial leaves that are conspicuously larger and
more hyaline than those on European material
examined" (Steere & Scotter 1978).
Although Macoun 190 was not available in the
loan received from CANM, three other North American
fruiting specimens were examined: Alberta, John
Macoun, June 27, 1904 (CANM); B.C., Lake of
Hanging Glaciers, Wilmer, July 21, 1928, MacFadden
4252 (NY); and also what is apparently an isotype of
Tortella inclinatula: B.C., Illicillewaet near Revelstoke,
May 27, 1890, Macoun 188 (NY). These were
compared with fruiting specimens of T. inclinata from
Europe (Strasbourg in western France, Switzerland and
Saxony in eastern Germany) among the W. P. Schimper
duplicates at BUF. No significant transoceanic
differences between the perichaetial leaves of these
plants were found. None of the American perichaetial
leaves exceeded those of the European ones excepting
one specimen (Macoun) in which the leaves were
perhaps 0.4 mm longer, an unimpressive magnitude of
difference. The laminae of the perichaetial leaves appear
white-hyaline in all specimens even at low
magnification. If the American material is different
from European specimens, the perichaetial leaves are
not decisive.
The strikingly differentiated perichaetial leaves
of Tortella inclinata var. inclinata only occur in
association with fertilized archegonia. When adjacent
perichaetiate unfertilized stems in specimens with
fertilized stems were examined, the perichaetial leaves
were less distinct from the stem leaves—for example,
they were not longer. Numerous specimens of
unfertilized perichaetiate plants of the var. densa from
North America showed much variability of the
perichaetial leaves but nothing to distinguish them from
those of unfertilized, perichaetiate var. inclinata.
In Tortella inclinata var. inclinata the
setaceous perichaetial leaves may be conspicuous on
dry stems where they rise more stiffly above the curled
stem leaves—as is true of those of T. alpicola, T.
fragilis and T. tortuosa. Such perichaetiate plants,
though uncommon, are easy to confuse with sterile or
fertile T. fragilis, but the setaceous leaves of that species
have propaguloid modifications in the apex whether
barren or fertile. Fertile T. inclinata var. inclinata has
also been confused with T. tortuosa but in the latter
species the lower leaves are also long-mucronate. The
lower leaves in T. inclinata var. inclinata are all
relatively blunt or cucullate.
The presence in some perichaetial leaves (with
fertilized archegonia) of an interrupted border of
elongate, thick-walled smooth cells in the distal portion
of the leaf is reminiscent of perichaetial leaves of
Tortella tortuosa where this character is more
pronounced. This characteristic is very important in the
subulate-propaguloid leaves of both sterile and fertile
(perichaetial) leaves of T. fragilis and seems to
contribute to the rigidity of the leaves that possess these
borders in all three species.