SIEVE ELEMENTS IN THE MORPHOLOGICALLY REDUCED MISTLETOE, VISCUM MINIMUM HARVEY (VISCACEAE)

The absence of phloem in some Viscaceae may be a direct result of morphological reduction. Viscum minimum is a highly reduced, South African mistletoe that parasitizes Euphorbia. The aerial portions of this species are 2–3 mm long and consist of only 1–2 intemodes with a terminal triad of flowers. The collateral vascular bundles are composed of tracheary elements, parenchyma, and sieve tubes with associated companion cells. The sieve‐tube members are similar to those described from other angiosperms, exhibiting simple sieve plates, P‐protein, stacks of ER, plastids, and mitochondria. The morphological reduction of V. minimum thus is not associated with a loss of phloic elements in contrast to other reduced viscaceous mistletoes.