Platydictya

Plants very small, light to dark green or brownish. Stems freely and irregularly branched; hyalodermis absent, central strand narrow or absent; paraphyllia absent; rhizoids or rhizoid initials below or at abaxial leaf insertion, or axillary, rarely forming tomentum, slightly branched, smooth or granular-papillose; axillary hair distal cells 1 or 2, hyaline. Stem leaves erect-appressed to loosely spreading, sometimes subsecund, lanceolate, not plicate, very small, 0.1–0.3(–0.5) mm; base not decurrent; margins plane, entire to serrulate, limbidia absent; apex acuminate, acumen plane; ecostate or costa double, very short, indistinct; alar cells scarcely differentiated to subquadrate, region small, inconspicuous, along basal margins; medial laminal cells subquadrate, oblong-rhombic, or short-rhomboidal; marginal cells 1-stratose. Sexual condition autoicous or dioicous. Capsule erect or variously inclined, oblong-cylindric to oblong-obovoid, symmetric or asymmetric; peristome perfect or somewhat specialized; exostome margins entire or dentate distally; endostome cilia absent or 1–3, rudimentary to well developed. Spores 8–13 µm.

Distribution

North America, South America, Europe, Asia.

Discussion

Species 10 (4 in the flora).

Platydictya resembles Amblystegium but is smaller and has virtually ecostate leaves. The capsule is variously inclined and asymmetric but not slender-cylindric, curved-asymmetric, or greatly contracted below the mouth and at the neck when dry. The genus is placed in Amblystegiaceae despite its ecostate, often secund leaves that suggest an alliance with Hypnaceae. The treatment by L. S. Cheney (1897) of Amblystegium, in a broad sense, is a useful reference for the species of Platydictya. Plants of Platydictya have creeping stems, slightly concave leaves, and finely papillose spores.

Selected References

None.

Lower Taxa

Platydictya confervoides, Platydictya jungermannioides, Platydictya minutissima, Platydictya subtilis

Key

1	Rhizoids axillary, purplish and granular-papillose at least when young; branching angle narrow, branches easily detached.	Platydictya jungermannioides
1	Rhizoids below or at abaxial leaf insertion, red-brown, smooth; branching angle wide, branches firmly attached	> 2
2	Distal laminal cells 2-3(-4):1.	Platydictya confervoides
2	Distal laminal cells (2-)3-6:1	> 3
3	Leaf margins entire or nearly so; perichaetial leaf margins entire; capsules erect or nearly so.	Platydictya subtilis
3	Leaf margins entire at insertion, serrulate elsewhere; perichaetial leaf margins coarsely dentate distally; capsules inclined, horizontal, or sometimes suberect.	Platydictya minutissima