Orthotrichum Hedwig, 1801

Nickte Mendez has revised this key, adding photographs to each couplet. We recommend her version over the 2004 key below: http://paulsiriwilson.space/orthotrichum/


Key to Orthotrichum Etc.

The plants included in this section are easily recognized by their sporophytes and associated structures: calyptra often hairy and plicate, capsule immersed or exserted on a short seta; capsule often sulcate and strangulate. Almost all species of Orthotrichum and Ulota are autoicous, and they are usually with sporophytes when collected.

Species included in this key are all in Orthotrichaceae:
Orthotrichum affine Bridel
Orthotrichum alpestre Hornschuch in Bruch & W. P. Schimper
Orthotrichum anomalum Hedwig, not known from CA
Orthotrichum bolanderi Sullivant
Orthotrichum consimile Mitten
Orthotrichum coulteri Mitten, recognized from CA since 2004
Orthotrichum cupulatum Bridel
Orthotrichum diaphanum Schrader ex Bridel
Orthotrichum euryphyllum Venturi
Orthotrichum flowersii Vitt
Orthotrichum hallii Sullivant & Lesquereux
Orthotrichum holzingeri Renauld & Cardot in Holzinger
Orthotrichum kellmanii D. H. Norris, Shevock & Goffinet, recognized from CA since 2004
Orthotrichum laevigatum J. E. Zetterstedt
Orthotrichum lyellii W. J. Hooker & Taylor
Orthotrichum macounii Austin
Orthotrichum norrisii F. Lara, R. Medina & Garilleti, recognized from CA since 2004
Orthotrichum obtusifolium Bridel
Orthotrichum pallens Bruch ex Bridel
Orthotrichum papillosum Hampe
Orthotrichum pellucidum Lindberg
Orthotrichum praemorsum Venturi in Röll
Orthotrichum pulchellum Brunt. in J. E. Smith & Sowerby
Orthotrichum pumilum Sw.
Orthotrichum pylaisii Bridel
Orthotrichum rivulare Turner
Orthotrichum rupestre Schleicher ex Schwägrichen
Orthotrichum schimperi Hammar, to some synonymous with Orthotrichum pumilum
Orthotrichum shawii Wilson, recognized from CA since 2004
Orthotrichum shevockii Lewinsky-Haapasaari & Norris
Orthotrichum speciosum Nees in Sturm
Orthotrichum spjutii Norris & Vitt
Orthotrichum striatum Hedwig
Orthotrichum tenellum Bruch ex Bridel
Orthotrichum texanum Sullivant & Lesquereux
Orthotrichum underwoodii F. Lara, Gariletti & Mazimpaka
Ulota megalospora Venturi in Röll
Ulota obtusiuscula C. Müller Hal. & Kindberg in Macoun
Ulota phyllantha Bridel
Zygodon rupestris W. P. Schimper ex Lorentz

Work with Orthotrichum normally requires examination of the epidermal cells of the capsule (exothecial cells) as well as features of the peristome. A longitudinal section of the capsule can be placed under a cover slip on a slide, boiled with the heat of a match, and examined under the compound microscope. There will always be a few stomates, and these may be surficial (phaneroporous) or sunken in a pit surrounded by thick-walled subsidiary cells (cryptoporous). It is especially easy to see the cryptoporous stomates because the subsidiary cell complex forms what appears to be small blisters, and these can usually be sensed even with a hand-lens. It may be more difficult to see the paired and green guard cells of the phaneroporous species, but they will be found with searching, especially near the base of the urn.

A number of important taxonomic features of capsules may be seen even with a hand lens. Are the exostome teeth erect, or are they curved outward and downward along the capsule mouth? This feature will be obvious with the caveat that newly deoperculate capsules will have the teeth erect before they take their eventual place in a recurved position. Are there endostome segments Here it is best to look at a newly deoperculate capsule as the fragile segments may be lost with age. Are the capsules sulcate? Here, an older capsule is best because the longitudinal ridges of a sulcate capsule may be obscured when the capsule is young. Are the capsules strangulate? The shrinking of the capsule immediately below the mouth is also a feature of the older capsule. The hairiness of the calyptra is easily seen with a hand-lens. The majority of the Orthotrichum species with glabrous or sparsely hairy calyptrae have cryptoporous stomates. Orthotrichum normally has rather short setae, and the degree of exsertion of the capsule should be gauged. A capsule is immersed if the longer perichaetial leaves extend beyond the capsule mouth. It is emergent if the longer perichaetial leaves extend to the level of the capsule. It is exserted if the seta is longer than any of the perichaetial leaves.

A. Leaf margins serrate with multicellular teeth; fertile plants polysetous with seta mostly more than 2 cm long ..... Ptychomitrium
A. Margins entire to serrulate .....B

B. Apex of leaf filiform with about 2-5 isodiametric to short- rectangular cells in a uniseriate apex .....C
B. Apex of leaf not uniseriate .....D

C. Plant stoloniferous with prostrate axes possessing abundant red-brown rhizoids; axillary gemmae absent; erect branches short, not at all hamate when dry; median leaf cells pluripapillose with papillae blunt and covering most of cell .....Ulota: U. megalospora
C. Plant erect and tufted, heavily gemmiparous in leaf axils; stem apices of dry plant strongly hamate; median leaf cells pluripapillose with papillae sharp and punctiform .....Zygodon: Z. rupestris

D. Basal marginal cells quadrate to very short rectangular, abruptly differentiated in several rows from the more elongate interior basal cells; capsules exserted with a long and well-demarcated neck; stomates phaneroporous .....E
D. Basal marginal cells not so abruptly demarcated; capsules and stomates various .....F

E. Apex of upper leaves with a reddish-brown cluster of septate gemmae; plant found only within a mile or so of the ocean .....Ulota: U. phyllantha
E. Apex of leaves not gemmiparous; plant more widely distributed .....Ulota: U. obtusiuscula

F. Leaves with the suprabasal, perimarginal cells having high, pointed papillae inserted not on the lumen but on end and lateral walls; plant dioicous with leaf apices either very long and somewhat flexuose when dry or with that apex bluntly eroded by gemma production .....G
F. Leaves without such a papillar arrangement; plant monoicous with leaf apices not usually long and flexuose; gemma production various .....H

G. Plant usually with dense gemmae on upper lamina and costa of most of the upper leaves; leaves not long-acuminate .....Orthotrichum lyellii
G. Plant without gemmae; leaves usually long-acuminate, often with elongate cells in a slightly serrulate acumen .....Orthotrichum papillosum

H. Leaves crispate when dry; plant growing as small tufts mainly on twigs of shrub and trees in the northwest of California; capsule with cryptoporous stomates .....I
H. Leaves erect and imbricate when dry; habit and stomate position of plant various .....J

I. Exostome red .....Orthotrichum pulchellum
I. Exostome white .....Orthotrichum consimile, the leaves are not as convincingly crispate as one might hope, a wrong turn at H will lead to O. tenellum.

J. Margins incurved to plane throughout .....K
J. Margins recurved to revolute at least at the base and usually through most of the leaf .....L

K. Plant blackish; leaf lamina bistratose; growing on moderately dry rocks .....Orthotrichum bolanderi, another species with bistratose leaves is O. hallii
K. Plant green, often with a reddish-brown cast; lamina unistratose; growing on trees in mountains often near watercourses .....Orthotrichum obtusifolium

L. Stomata phaneroporous; basal cells elongate and somewhat porose or with sinuose walls .....M
L. Stomata cryptoporous; basal cells short-rectangular with evenly thickened walls .....W

M. Leaves smooth; peristome smooth; calyptra glabrous; very localized plant of volcanic plateaus in northeastern California and in neighboring states to the northeast .....Orthotrichum holzingeri
M. Leaves strongly papillose; peristome minutely to high papillose; calyptra with abundant hairs .....N

N. Capsule smooth, shorter than 4:1 .....Orthotrichum striatum
N. Capsule ribbed at least in upper half; capsule longer .....O

O. Peristome reduced to a few basal plates; plant glaucous due to the very high multifid papillae; adaxial face of costa covered by laminal cells in at least the distal 1/3 of leaf; spores to 11 µm in diameter .....Orthotrichum spjutii
O. Peristome fully developed; plant not glaucous; adaxial face of costa with elongate cells throughout; spores markedly larger .....P

P. Endostome at least in part two cells wide, more than half as long as exostome; mostly epiphytic plants with cylindric capsules .....Q
P. Endostome mostly not present or quite abortive; mostly rupestral plants with oblong capsules .....R

Q. Capsule immersed, strangulate and strongly ribbed from near the mouth to the base; exostome teeth not fenestrate .....Orthotrichum affine
Q. Capsule emergent, ribbed only in distal half; exostome teeth usually fenestrate .....Orthotrichum speciosum

R. Sporophyte immersed so that the apices of the nearest perichaetial leaves are above the mouth of the capsule .....S
R. Sporophyte emergent to exserted .....T

S. Plant growing as small, closely aggregated, tufts on rocks or trees; exostome densely papillose .....Orthotrichum texanum
S. Plant growing as rather large, loose mats primarily on rocks; exostome low papillose to almost smooth .....Orthotrichum rupestre

T. Peristome erect to spreading when dry; endostome segments essentially absent .....U
T. Peristome reflexed and often broken but with the bases still showing that reflexing; endostome segments sometimes present .....V

U. Capsule ovate to short-oblong, exserted or nearly so; exostome teeth 16 but sometimes tardily separating from an initial 8 pairs .....Orthotrichum pylaisii
U. Capsule cylindric, about 1/2 emergent; exostome teeth 8, even in older capsules; leaf apices acuminate to cuspidate, often bleached .....Orthotrichum praemorsum

V. Leaves bluntly acute to obtuse; median cells mostly rather low papillose; adaxial surface of costa above its middle showing elongate to linear, thick-walled cells .....Orthotrichum laevigatum
V. Leaves long-acuminate to narrowly acute; median cells with papillar salients at least as high as 1/2 the cell thickness; adaxial surface of costa above its middle covered with cells like those of the adjacent lamina .....Orthotrichum macounii

W. Leaves terminating in a hyaline awn .....Orthotrichum diaphanum
W. Leaves without hyaline awn .....X

X. Plant strongly heterophyllous with the vegetative leaves blunt and ligulate but with the leaves below the perichaetium acuminate and lanceolate, markedly enlarged relative to vegetative leaves; exostome erect to somewhat spreading, densely spiculate-papillose; endostome very short ..... Orthotrichum species A
X. Plant isophyllous without differentiation between the vegetative leaves and perichaetial leaves; peristome with exostome reflexed and papillose with endostome obvious or erect and striate with endostome very short to absent .....Y

Y. Exostome erect or spreading, with the striate ridges on the dorsal face resembling a fingerprint; endostome absent; leaves often bistratose or with bistratose streaks; plants consistently epipetric .....Z
Y. Exostome reflexed to recurved, papillose to papillose-striate but never with a fingerprint-like pattern; endostome present; leaves unistratose; most of the species epiphytic .....AC

Z. Capsule exserted and cylindrical, mostly with 8 long ribs alternating with 8 short ones .....Orthotrichum anomalum not known from CA
Z. Capsule immersed to emergent; with 8 or 16 ribs .....AA

AA. Capsule with 16 ribs; leaves only remotely keeled, acute .....Orthotrichum cupulatum
AA. Capsule with 8 ribs; leaves distally keeled, obtuse to bluntly acute .....AB

AB. Leaves unistratose, stiff, ligulate with the apices incurved; papillae high and forked; plant glaucous .....Orthotrichum pellucidum
AB. Leaves bistratose, lanceolate and loosely appressed; papillae low, conical and not forked; plant green to dark green .....Orthotrichum hallii

AC. Leaf apex rounded-obtuse and often irregularly serrate; leaves smooth to inconspicuously papillose; plant of seasonally inundated rocks or tree bases .....AD
AC. Leaf apex acute to acuminate or mucronate, entire to, at most, papillose-crenulate; leaves smooth to densely papillose; plant epiphytic or occasionally epipetric on dry rocks .....AE

AD. Leaves very dark green to nearly black; median cells mostly more than 15 µm in diameter; costa terete in cross-section; plant of rocks on stream heads in exposed dry to semi-desert sites .....Orthotrichum euryphyllum
AD. Leaves rich dark green, sometimes black on older portions; median cells mostly to 12 µm; costa flat in cross-section; on trees and rocks in frequently flooded areas of stream flood- plains .....Orthotrichum rivulare

AE. Leaf margins bistratose; capsules immersed with seta less than 0.5 mm long .....Orthotrichum shevockii
AE. Leaf margins unistratose or leaf lamina bistratose throughout; capsules immersed to emergent .....AF

AF. Sporophyte immersed so that the apices of the nearest perichaetial leaves are above the mouth of the capsule .....AG
AF. Sporophyte emergent to exserted .....AI

AG. Capsules sulcate throughout, short-cylindric; endostome with 16 separate segments .....Orthotrichum underwoodii
AG. Capsules lightly sulcate primarily toward the strangulate mouth, mostly oblong in shape; endostome with 8 segments .....AG

AH. Leaves oblong-ovate, carinate in the rounded obtuse apex, often mucronate .....Orthotrichum flowersii
AH. Leaves ovate-lanceolate, not at all carinate in the acute, usually apiculate apex .....Orthotrichum pumilum

AI. Calyptra with hairs prorate to papillose .....Orthotrichum alpestre
AI. Calyptra with hairs absent or smooth .....AJ

AJ. Subsidiary cells around stomates without thickened radial walls, thus with guard cells only somewhat covered by those subsidiary cells; leaves somewhat decurrent .....Orthotrichum pallens
AJ. Subsidiary cells with strongly thickened radial walls that obscure the outline of the guard cells below; leaves not at all decurrent .....Orthotrichum tenellum