Some ultrastructural aspects of the stem phloem in Phacellaria (Santalaceae) and Korthalsella (Viscaceae)

SUMMARY We present documentation of the occurrence of normal sieve‐tube members in Korthalsella dacrydii (Ridley) Danser and K. japonica (Thunb.) Engler (Viscaceae) and Phacellaria malayana Ridley (Santalaceae), three squamate parasites. From this we may now state that morphological reduction (paricularly the squamate condition and small size) in Santalales is not necessarily correlated with the evolutionary disappearance of sieve elements; the latter condition is probably unique to some species of Arceuthobium (Viscaceae). Sieve‐tube plastids in Phacellaria are comparable to the S‐type plastids known from all other known parasitic angiosperms. In Korthalsella sieve‐tube members, regularly stacked and corrugated endoplasmic reticulum complexes are present as known from studies of Ranunculaceae and Papaveraceae.