Ditrichum pallidum
Ditrichum ambiguum
golden thread moss, pale ditrichum moss
ambiguous ditrichum moss
short, to 0.5(–1) cm, usually simple.
0.7–2 cm, with a few reddish rhizoids at the base.
erect-spreading to subsecund, flexuose-contorted when dry, to 7 mm;
from a short ovate-lanceolate and ± sheathing base gradually or rather shortly narrowed to an elongate subula, lamina 2-stratose distally;
margins erect, becoming serrulate towards the apex, 1-stratose proximally, 2-stratose in the subula;
costa rather thin and narrow at the base, broader distally and occupying most of the base of the subula, excurrent, in section with a broad band of guide cells and shallow adaxial and abaxial stereid bands;
cells of the leaf base rectangular to oblong-hexagonal, narrowed towards the margin and forming a ± distinct hyaline zone, elongate-rectangular in distal leaf base and subula.
erect-spreading, somewhat crisped when dry, 1.5–4.5 mm, lanceolate to linear-lanceolate, channelled, lamina with a few scattered 2-stratose cells midway between margins and costa in median to distal part of leaf;
margins broadly recurved from the base to near mid lamina, weakly to strongly serrulate from mid lamina to apex, entire or serrulate at the somewhat blunt apex, 2-stratose distally and sometimes extending inward for several cells;
costa distinct, percurrent, occupying 1/6–1/3 the width of the leaf base;
lamina cells thick-walled, distal cells quadrate, irregularly subquadrate to short-rectangular, 8–24 × 4–8 µm, becoming broader and longer near the base.
yellow or sometimes reddish brown near base, elongate, to 4 cm or occasionally longer, flexuose.
red, 1–2 cm, erect.
autoicous;
perigonia axillary;
perichaetial leaves shorter than stem leaves, the base not sheathing.
dioicous.
suberect to somewhat inclined, yellow to brownish yellow, reddish brown with age, subcylindric, with a broadened base tapering gradually to a narrowed mouth, 1–2.5 mm, slightly asymmetric, weakly furrowed when dry and empty;
operculum conic-rostrate, to about 0.8 mm;
peristome 300–800 µm, pale brown to yellowish orange, 2-fid to a very short basal membrane, densely spiculose throughout.
erect, usually straight and symmetric or sometimes slightly curved, dark brown or reddish, cylindric, 1.5–3(–3.2) mm, occasionally slightly enlarged at base;
operculum rostrate, 0.4–0.8 mm;
peristome red, 200–500(–800) µm, twisted when dry, teeth divided to near base into two equal filaments, strongly papillose to spiculose.
long-cucullate.
rounded to obscurely tetrahedral, 15–30 µm, coarsely and sparsely papillose, brown.
round, 6–13 µm, appearing smooth to minutely papillose.
asexual reproduction unknown.
asexual reproduction unknown.
Ditrichum pallidum
Ditrichum ambiguum
When Ditrichum pallidum is fruiting, the long, yellow setae are distinctive. The slightly asymmetric capsule and the long, spiculose peristome teeth are similar to those of D. difficile (Duby) Fleischer, a widespread, common species occurring in Mexico, Central and South America as well as elsewhere throughout the world, and D. rhynchostegium. However, the spores of all three species are easily distinguished. Spores of D. difficile are finely papillose-verrucose and 12–18(–20) µm; those of D. rhynchostegium are vermicularly papillose-verrucose and 11–15(–18) µm; those of D. pallidum are larger, 15–30 µm, and the exine ornamentation coarsely and openly papillose.
Herbarium specimens of Ditrichum pallidum and D. rhynchostegium are sometimes misidentified. If fruiting, the orange to reddish seta of D. rhynchostegium will immediately distinguish it from D. pallidum with its yellowish seta. Also, spores of D. rhynchostegium have a distinctly vermicular ornamentation and are smaller. The operculum of D. pallidum is about half the length of that of D. rhynchostegium. Vegetatively, plants of D. pallidum have short stems and the leaf base is often ovate to ovate-lanceolate, being gradually narrowed to the subula. On the other hand, plants of D. rhynchostegium have longer stems and the leaf base is oblong-ovate and abruptly narrowed to the subula. L. E. Anderson and V. S. Bryan (1958) discussed the similarity of D. currituckii and D. pallidum, but maintained them as distinct species. H. A. Crum and Anderson (1980–1983) considered D. currituckii to be a variant form of D. pallidum having shorter capsules and peristomes, slightly shorter leaves with the costa somewhat broader at the base. The morphological and cytological differences were considered by Crum and Anderson (1981) to be insufficient to warrant separation.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Ditrichum ambiguum, a western species, is very close to an eastern species, D. tortuloides, but differs in the following morphological characters: stems often branched and taller, 7–20 mm compared to the shorter, 2–5 mm, usually simple stems of D. tortuloides; leaf margins broadly recurved, entire or serrulate at a somewhat blunt apex, compared to the narrowly recurved, serrate to strongly serrate margins from mid-leaf to an acute apex in D. tortuloides; leaf laminae with 2-stratose margins and occasional 2-stratose regions between the margins and the costa in the middle to distal half of the leaf, compared to the 2-stratose regions only on the margins in D. tortuloides; capsules dark brown to reddish, 1.5–3.2 × 0.2–0.5 mm, straight and symmetric to rarely slightly arcuate with an occasionally slightly swollen base, compared to the yellow or light brown, 1–2.5 × 0.2–0.3 mm, curved and asymmetric capsules often with a swollen base in D. tortuloides. The geographic ranges of the two taxa are quite disparate. The species has been reported outside North America by B. H. Allen (1994), from Guatemala and Panama.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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