Banded tubes are a type of

phytoclast Phytoclasts are microscopic plant fragments present in the fossil record, usually found in palynological preparations and acid macerations, and include banded tubes and various nematophytes. References Fossil record of plants Prehistoric ...

consisting of micrometre-scale tubes with a banded internal ornamentation, and known from terrestrial/freshwater settings from the Early Silurian onwards. The bands on the walls were an early improvisation to aid the easy flow of water, and served as

tracheid A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through the ...

s, although they are not equivalent in their construction. Banded tubes were lignified, giving them a more rigid structure than

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater ''Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds, ...

, allowing them to cope with higher levels of water pressure. Banded tubes have a markedly different ultrastructure from plant tracheids, and display a wide variety of wall structures, which implies that they were produced by a variety of different organisms, or perhaps were widely variable within a single

nematophyte The Nematophyta or nematophytes are a paraphyletic group of land organisms, probably including some plants as well as algae known only from the fossil record, from the Silurian period until the early Devonian Rhynie chert. The type genus ''Nem ...

-like organism. Proposed functions include water transport, feeding (cf. fungal hyphae), and anchorage (cf. rhizoids). Some banded tubes can be assigned to genera such as '' Nematoplexus'' and ''

Nematasketum ''Nematasketum'' (sometimes incorrectly spelt nematosketum) is a nematophyte with internally thickened tubes. It is thought to be terrestrial or freshwater, and seems to be aligned with the fungi. References Silurian plants {{siluri ...

'', in the latter, they occur in bundles alongside other tubes; ''Nematasketum'' is probably fungal.

References

Fossil record of plants {{Paleobotany-stub