Anatomy and mycotrophy of the achlorophyllous Afrothismia winkleri

Afrothismia winkleri develops fleshy rhizomes, densely covered with small r oot tubercles, narrowing to filiform roots with age. The exclusively intrac ellular mycorrhizal fungus has distinct morphologies in different tissues o f the plant. In the filiform root the hyphae grow straight and vesicles are borne on short hyphal stalks. The straight hyphae are present in the epide rmis of the root tubercles, but change to loosely coiled and swollen hyphae in the rhizome tissue. No penetration from epidermis to root cortex was fo und. From the rhizome, a separating cell layer permits only one or rarely t wo hyphal penetrations into the cortex of each root tubercle. The hyphae pr oceed apically within the root hypodermis in a spiral row of distinctively coiled hyphae, branches of which colonize the inner root cortex. In the inn er root cortex the hyphal coils degenerate to amorphous clumps. In older ro ots the cortex itself also deteriorates, but epidermis, hypodermis, endoder mis and central cylinder persist. The mycorrhizal pattern in A. winkleri is interpreted as an elaborate exploitation system whereby the fungus provide s carbon and nutrients to the plant and, simultaneously but spatially disti nct, its hyphae are used to translocate and store the matter within the pla nt. Several features indicate that the endophyte is an arbuscular mycorrhiz al fungus.