Abstract
Flowers of most Ericaceae are characterized by pentamery and sympetaly. Empetrum is one of the members of Ericaceae that deviate from this flower groundplan. Due to differences in floral morphology, earlier classifications places Empetrum in a distinct family, Empetraceae belonging to various orders. Perianth of Empetrum is composed by two trimerous whorls of free phyllomes. Different authors interpret it as either simple (with tepals) or double (with sepias and petals). The paper presents scanning electron microscopic data on flower development in Empetrum hermaphroditum. Developmental data suggest that the perianth should be interpreted as double one. Petals are free in anthetic flower and rudiments of corolla tube are not found in early stages of flower development. In this respect, Empetrum differs from some other Ericaceae with free petals in anthetic flowers (such as Rhodonendron tomentosum- Leins, 1964) where rudiments of corolla tube can be traced early in development. In both cases, secondary loss of sympetaly should be assumed. In contrast to another, unrelated genus of Ericaceae bearing flowers with three petals (Tripetaleia-Nishino, 1988) no signs of 'cryptic pentamery' can be traced in flowers of Empetrum. Different patterns of carpel arrangement are documented in Empetrum. Polymerous gynoecium of Empetrum is interpreted as an apomorphic character state derived from a gynoecium isomerous to perianth whorls.
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