NAME Laevitubulus laxus
AGE Late Ordovician to Early Devonian.   AGE span: 460.9...397.5 mya
K&J CLASSIFICATION (2000) Fungi Imperfecti, Mycelia sterilia.
FIGURE(S)
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Pl.30fig.12.jpg
FIGURE REFERENCE Burgess ND, Edwards D. 1991. Classification of uppermost Ordovician to Lower Devonian tubular and filamentous macerals from the Anglo-Welsh Basin; Botanical Journal of the Linnean Society, v. 106, p. 41-66.
SPECIES, AUTHORITY L. laxus Burgess & Edwards 1991, p. 51, fig. 17.
LOCATION Anglo-Welsh Basin, Great Britain.
ORIG DESCRIPTION* Tubes 5-7.5 µm in diameter, may branch occasionally at an acute angle, wall 0.5-1.5 µm thick. Specimens usually recovered in loosely aggregated wefts, although isolated examples are occasionally found. These tubes are a mid-brown color in thermally immature samples and have uniformly thickened walls ca. 1 µm thick (fig. 21). They are at least 800 µm long, and branch occasionally. Branches are 20-100 µm apart and branching is usually at an acute angle (fig. 17). Such tubes are generally found in loosely aggregated monotypic wefts where individual tubes are usually randomly orientated but occasionally have a preferred orientation. Occasional specimens found isolated (fig. 18). No end walls, or tapering indicating a termination, have been seen. Under SEM observation the surface of many tubes appears microgranulate (fig. 21). Swellings in tubes illustrated in fig. 19 are believed to be caused by pyrite crystals within the tubes.
COMMENTS* Edwards (1982) recorded wefts composed of similar branched tubes 2-6 µm in diameter (p. 241) from the Late Ludlow of Wales, and similar although slightly wider forms (ca. 9 µm) from the Late Wenlock of Ireland (Edwards et al., 1983). The tube weft described as specimen 5 of Nematothallus Lang (1937; pl. 12, figs. 84-87) has tubes of similar size and branching form. Lang thought that his specimen may have been: "another form of Nematothallus". Furthermore, Strother (1988) has described extensive (up to 20 mm long) Nematothallus wefts composed of this species from the Bloomsberg Formation, Pennsylvania, USA., emphasizing the probable nematophytalean origin for most L. laxus specimens, but the derivation of all from this source cannot be proven.

Derivation: from Latin laxus-loose, referring to the loosely aggregated wefts of this species.
PUBLICATION REFERENCE Burgess ND, Edwards D. 1991. Classification of uppermost Ordovician to Lower Devonian tubular and filamentous macerals from the Anglo-Welsh Basin; Botanical Journal of the Linnean Society, v. 106, p. 41-66.
K&J REMARKS
TYPE
ALL NAMES (Including synonyms) Laevitubulus laxus
SERIAL NUMBER 884
PUBLIC COMMENTS
 *For source, see Publication Reference.