re-evaluation of tortella - Missouri Botanical Garden

two narrower inner perichaetial leaves whose laminae
are only somewhat narrower in the distal region, this
character exaggerated by the presence of a longer mucro
on most of the leaves of the elongate forms and by
incurved distal margins. Elongate forms of T. humilis in
North America share this characteristic as well.
Occasionally the inner perichaetial leaves may be rather
abruptly contracted above a more or less sheathing base,
forming a narrow limb as in some leaves of the type of
T. japonica. However, this may also be seen in
specimens of the short-leaved forms of T. humilis in
North America as well and is considered here to be part
of the normal variation in the species. The perichaetial
leaves of T. humilis in either long or short forms are
considered here to be undifferentiated. Differentiated
perichaetial leaves in the present paper are different
almost in kind from the stem leaves: primarily with a
long, naked extension of the costa into an awn, such as
occurs in T. tortuosa, T. inclinata var. inclinata, T.
alpicola and T. fragilis.
Saito also did not mention that the proximal
cells interior to the proximal marginal cells gradually
intergrade with the distal laminal cells, as is
characteristic of Tortella humilis. In the elongated forms
of North American material, especially in leaves toward
the stem apex, the longer leaves have a more
distinctively V-shaped differentiation of the proximal
cells. This is true in the longest leaves of intermediate
American forms, such as in the outer perichaetial leaves,
whereas the intergradation is less distinct in shorter
leaves, and merely U-shaped in very short-leaved
material. Unfortunately, the variable Trichostomum
tenuirostre also has a U-shaped differentiated proximal
region very similar to specimens of both Tortella
japonica and T. humilis, and, as in Saito's illustration,
the differentiated proximal cells of Trichostomum
tenuirostre do extend up the margins in various degrees,
just as in the genus Tortella. While Tortella japonica
may often be tomentose, Trichostomum tenuirostre is
never so.
It is possible that descriptions of Tortella
japonica by Saito (1975) and Noguchi (1988) include to
some degree the characteristics of Trichostomum
tenuirostre (= Oxystegus cylindricus (Brid.) Hilp.), a
species which may be nearly indistinguishable from
sterile specimens of the elongate-leaved Tortella
humilis, and whose ranges and substrates overlap. In
fertile specimens the best distinction is in the nearly
always demonstrable autoicous bud in the latter species
and its long-twisted peristomes in fruiting material. The
former species is dioicous with comparatively shorterect
teeth. In fact, the leaf shape of the plant illustrated
for Trichostomum tenuirostre by Saito (1975) resembles
closely that of typical Tortella humilis, complete with
the indication of the "U" shape of differentiated
proximal cells. Trichostomum tenuirostre also has a
more elongate stem (to 15 mm), usually more than twice
the length of the stemless to short-stemmed Tortella
japonica (to 7 mm).
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Note that, although Saito (1975) indicated
that Tortella japonica has a stem central strand and that
Trichostomum tenuirostre does not, the latter species
does, in many cases, have one, both in the Japanese
material examined and as attributed to that species in
the United States (Flowers 1973) and in Europe (Hilpert
1933).
When both species are sterile, they may be
distinguished by the relatively shorter stem of Tortella
humilis (to 7 mm), its rosulate habit, its variable
tomentum and its leaf edge firm and orderly (regular),
as opposed to the more elongate stem of Trichostomum
tenuirostre (to 15 mm), the leaves more loosely
disposed on the stem, its lack of tomentum and its leaf
edge often showing a scalloping or lobing edge
indicating zones of weakness; there is greater fragility
of the leaf lamina and occasional obscure and distant
marginal teeth in the distal leaf region. Also a
distinctive V-shaped proximal cell region of Tortella
humilis may often be successfully found on the largest
leaves, whereas in Trichostomum tenuirostre this will
not occur.
The type of Tortella japonica represents a large
stature that even the ordinary representative specimens
in Japan do not approach, yet the type material (at PC)
has the same leaf shape as ordinary North American
material. Such large stature was duplicated in a
specimen from Ontario, Canada from the north shore of
Lake Huron, possessing a proliferation of branches, four
of which supported fertile perichaetia with a long stem
to 7 mm, the longest among variants on the margins of
the North American floral distribution.
In Zander's (1994d) description of Tortella
japonica from Mexico, he noted the "shiny upper part of
the costa, owing to smooth, elongate cells on the ventral
surface" contributed to the distinctiveness of the
Mexican specimens examined. However, he also
described the plants as having a "costa covered on the
adaxial surface in the middle of the leaf by quadrate,
papillose cells." In typical short-leaved Tortella humilis,
the quadrate cells on the adaxial surface of the costa
disappear toward the apex of the leaf—but this is
inconspicuous. In leaves significantly more elongate,
this region of elongate, smooth cells is also longer and
more conspicuous. The same comparison may be made
between short and very long leaves of Tortella tortuosa.
Clearly Tortella humilis, a widespread species
in the Northern and possibly Southern Hemisphere,
shows a plasticity not previously recognized. In North
America, it grades from short, broad plants in the
northcentral and eastern distribution, becoming more
gracile on its margins, especially to the south. Indeed,
upon review of examples at BUF used by Zander for the
Moss Flora of Mexico, nearly all of the Mexican
material of Tortella humilis is a "Tortella japonica"
facies similar to plants from Texas and the southern
American states. All other material seen in a small
sample of Mexican specimens at BUF, represents
minute plants that are sterile, or are possibly not
satisfactorily named.