KWIATKOWSKA, DOROTA. Institute of Botany, Wroclaw University, Kanonia 6/8, 50-328 Wroclaw, Poland. - Patterns of shoot primary structure related to phyllotaxis.
Patterns associated with phyllotaxis are: pseudowhorls; primary
vasculature; and wing pattern. Pseudowhorl pattern is imposed on the
arrangement of leaf primordia and results from the selective internode
elongation. Pseudowhorl is a group of successively initiated leaves,
all positioned at almost the same level. Adjacent pseudowhorls are
separated by a fully elongated internode. Number of leaves in a
pseudowhorl depends on the quality of phyllotaxis, but also on the
relation of leaf primordia size to the size of an apex dome, i.e.
primordia packing. When primordia are large, as in Anagallis
arvensis, this number equals the number of primordia on one
revolution of ontogenetic spiral. When they are small, their number
increases to a bigger member of the phyllotactic series, like in
Peperomia verticillata. In this particular species even when
phyllotaxis is truly whorled only every second internode elongates. It
results in the formation of pseudowhorls composed of leaves belonging
to two adjacent whorls. Another pattern closely related both to the
quality of phyllotaxis and to primordia packing is the pattern of
vascular sympodia. In primary vasculature of Anagallis shoots,
their number is defined for each particular leaf distribution but the
number of bundles composing individual sympodia is influenced by the
local variation in circumferential spacing of leaves. This in turn is
especially variable when phyllotaxis changes. The last pattern -
formed by wings on the stem surface, at first sight seems to be the
simple derivative of leaf primordia arrangement and elongation of
internodes: wings are continuous with margins of leaf blades. In
Anagallis however, wing pattern is to some extent autonomous.
Wings not connected with any leaf are often formed on the shoot
surface between the most widely separated leaves.
Key words: Anagallis arvensis, Peperomia verticillata, phyllotaxis, primary vasculature, pseudowhorls, stem wings