Notothylas orbicularis (Schweinitz) Sullivant, 1821

Cargill, D. Christine, 2016, Rare and peculiar hornworts: Notothylas orbicularis and N. javanica (Notothyladaceae), new genus and species records for Australia, Phytotaxa 275 (1), pp. 1-13 : 5-11

2. Notothylas orbicularis (Schweinitz) Sullivant in A. Gray, Musci Alleghaniensis, Exsicc. No. 290, [review] American

Journal of Science and Arts, Series 2, 1: 75. (1846)

Targionia orbicularis Schweinitz , Species Florae Americae Septentrionalis Cryptogamicae. 23, 1821.

Type: U.S.A.: North Carolina, Forsyth, Salem, on moist earth, L.D. Schweinita [sic] s.n. (holotype PH, n.v.).

Illustrations: J. Hasegawa, Acta Phytotaxonomica et Geobotanica. 30: 22 (1979); H. Stieperaere & H.W. Matcham, Journal of Bryology 29: 4 (2007).

Plants as scattered patches intermixed with other hornworts or bryophytes or in small gregarious mats, patent, unbranched or bifurcate, broadly fan-shaped to sub-orbicular, 2.0–8.0 mm long, up to 8.6 mm wide, lobes 0.5–1.9 mm wide, margins irregularly dissected; thallus green (RHSCC 143B yellow-green group) becoming pale grey-green (RHSCC 195A, 197A greyed-green group) upon drying. Thallus solid, ecostate, mid thallus up to 3 cells (150–225 μm) thick, gradually decreasing in thickness to a single cell at the margins, varying from shallowly fusiform to shallowly plano-convex in transverse section sometimes with shallow ventral keels. Dorsal surface smooth in most part but also with various outgrowths present over ventral involucres. Dorsal epidermal cells quadrate to heptagonal, 17.5–135 μm x 15–80 μm, internal cells 50–362.5 μm x 35–162.5 μm. Ventral epidermal cells quadrate to heptagonal, rarely octagonal, 20–162.5 μm x 17.5–72.5 μm. Ventral clefts absent. All epidermal cells with a single chloroplast, pyrenoid present. Nostoc colonies present, numerous, appearing as pale green or blue-green dots within the thallus. Rhizoids ventral, in patches, both hyaline and granular. Specialised asexual reproduction absent.

Monoicous, androecia in small clusters at the margins or along the centre line of each lobe or at apex of lobes, with one antheridium per cavity, white, baculate or spherical, jacket cells irregularly arranged, 105–180 x 60–125 μm, stalks not measured. Involucre ventral, horizontal, tubular and smooth or tubular and ridged at base, but becoming asymmetric distally, highly dissected, 1–3.2 mm long, 3–6 layers thick, epidermal surface smooth or ridged. Sporogone mainly ventral (only one plant found with sporogones on the dorsal surface as typically observed for this genus) and growing horizontally along thallus surface extending beyond thallus margin. Capsule emergent, spindle-shaped, frequently curved, 1.0– 14 mm long and 450–600 μm wide, two specialised sutures or valves running the length of the capsule, but also frequently with one or two partial sutures present, splitting along two valves and detached at the apex; bicoloured with epidermal cells bright orange, sutures or valves becoming red with maturity, foot easily detached, bulbous at end of stalk.Assimilative layer 2–3 cells thick, compressed, sporogenous layer of 2 rows, columella present, from 1.0– 2.05 mm long, 26 cell rows at base, reducing to 4–5 rows along most of its length. Epidermal cells of capsule polygonal and broadly elongate-rectangular, 37.5–100 μm x 15–32.5 μm, sometimes cells distinctly mamillate with mamilla up to 7.5 μm high varying in shape from broadly triangular to long and thin; walls thick (5–12.5 μm wide) with an elongate, narrow lumen (1.25–15 (–20) μm wide), stomata absent. Spores yellow to yellowish-brown or brown, hemispherical-tetrahedral in equatorial view, spherical in polar view, equatorial diameter 45–67.5 μm, polar height 25–35 μm. Spore with narrow equatorial cingulum, macro-ornamentation lacking on both distal and proximal surfaces, both distal and proximal surface micro-ornamentation vermiculate, proximal triradiate mark distinct, thin. Pseudoelaters present, translucent, brown, rectangular with irregular thickening bands, 32.5–90 μm long and 17.5–45 (–57.5) μm wide.

Plates 4–7 .

Distribution:—Cosmopolitan species found across the world, but rare in Australia, found so far only in the Wet Tropics of Queensland and the Kimberley region of Western Australia.

Specimens examined:— QUEENSLAND: Blencoe Creek, Kirrama Forest [now Kirrama NP], Herberton Shire, 22

May 1985, I.G. Stone MUCV 7239 p.p. (MELU); WESTERN AUSTRALIA: Lillimilura, Winjina Gorge, Kimberley,

3 May 1988, G.A.M. Scott s.n. (MELU 767). Etymology:—From the Latin ‘ orbicularis’ referring to the circular shape of the thallus.

Figures

PLATE 4. Notothylas orbicularis. a. Dorsal view of fertile plant.b. Ventral view of fertile plant, stained with toluidine blue. c.Apical view of capsule epidermis. d. View of the mid-section of a capsule showing the pigmented red valve cells. e. View of an open capsule showing the internal columella and the asymmetrical involucre. f. Single capsule showing the bulbous foot at the base. g.A single plant with mature antheridia (an) (arrow). h. Inset. Magnified image of single white antheridium per cavity. Images by D. C. Cargill.

PLATE 5. Notothylas orbicularis. a. Transverse section through the columella. b. Capsule epidermal cells illustrating the elongated thickwalled cells. c–d. SEM images of proximal and distal views of spores. e. Light microscope image of a spore. f. Pseudoelaters. Images by D. C. Cargill.

PLATE 6. Notothylas orbicularis. a. Dorsal view of plant. b. Ventral view of same plant illustrating ventral position of capsules. c. Dorsal view of a fertile plant. Black dots are Nosotoc colonies. d. Magnified view of capsule and highly dissected involucre. e. Transverse section through thallus showing large internal hypodermal cells sandwiched between dorsal and ventral epidermis. f. Dorsal epidermal cells. g. Ventral epidermal cells. Illustrations by D. C. Cargill.

PLATE 7. Notothylas orbicularis. a. Open sporophyte. b–c. Cells of the columella. d. Elongate, thick-walled cells of capsule epidermis (val=valve cells; ep=epidermal cells). e. Transverse section through columella. f. Internal cells of capsule below epidermal cells. g. Proximal views of two spores and two pseudoelaters with internal thickenings (ps=pseudoelater). Illustrations by D. C. Cargill.