Triuris hyalina, an unusual achlorphyllous plant, was investigated for subterranean morphology,
root anatomy and mycotrophy. Stems with scale leafs extend subterraneously to a depth of 15 cm. Pairs of
adventitious roots develop at the scale leafs and clumps of apparently radiating roots, formed by accumulations
of side shoot and scale leaf developments, occur. Roots consist of epidermis, short cell exodermis, three distinct
layers of cortex parenchyma, endodermis and an extremely reduced central cylinder with one or two central tracheidal
xylem elements.
The fungus associated with Triuris hyalina roots, exhibit thick walled, 6-9 µm thick, aseptate external hyphae.
It penetrates the epidermis by developing appressoria and enters the cortex solely through the short cells of the exodermis.
In the cortex cells, the aseptate hyphae start to coil. In the outer cortex layer hyphae are thin, frequently branched
and most densely coiled. In the middle cortex layer they are thicker, less densely coiled and mostly appear degenerated
to clumps of amorphous fungal material. The inner cortex layer rarely becomes colonized. Vesicles occur in the outer
and the middle cortex layers. This mycorrhizal pattern is interpreted as an adaption to attain a sustainable use from
the endophyte.
It is suggested that the mycorrhiza in Triuris hyalina be interpreted as a type of arbuscular mycorrhiza (AM).
Implications for systematics and ecology are discussed.
Key words: Triuris, Triuridaceae, root structure, anatomy, arbuscular mycorrhiza, myco-heterotrophy.
