KIM, INSUN. Biology Department, Keimyung University, Taegu 704-701, Korea. - Greatly reduced duckweed morphology with highly effective structural organization.
Morphologically, duckweeds are poorly differentiated hydrophytes that
only produce connected fronds with a single or multiple root system on
each frond. Such morphological reduction in small, free-floating
plants of Lemna and Spirodela has led to the speculation
of their simple anatomy. In the current study, complex structural
organization, in respect to the cellular differentiation, is revealed
within each organ of the Lemna and Spirodela plant body.
In particular, laterally connected translucent stalk cells, commonly
with polymorphic mitochondria, fibrillar supporting structures and
unevenly thickened walls are the most noticeable features. A distinct
boundary layer filled with fibrillar materials at the root-root cap
junction, chloroplasts having grana with 3-9 stacked thylakoids and
starch grains distributed throughout the plant are other interesting
structural attributes drawing attention in the study. In summary,
characteristics such as an entirely chlorenchymatous plant body,
poorly developed vescular tissue, well-established plasmodesmatal
connection, rapid vegetative reproduction, offspring protection,
aerenchyma formation, effective abscission in the connective stalk and
a well-organized root proper having a prominent root cap are clearly
demonstrated in these greatly reduced species. Such reduction and
differentiation of the plant body effectively contribute to the better
adaptation of smaller plants to superficial aquatic environments,
while enabling rapid growth.
Key words: adaptation, effective organization, Lemna, Spirodela, structural reduction