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| Home > Academics > Department Pages > Biology > Faculty > Chmielewski, Jerry G. > Research Interests |
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SYSTEMATICS OF ANTENNARIA
- The genus Antennaria is a dioecious member of the tribe
Inuleae and is distributed throughout the cold temperate and arctic
regions of the northern hemisphere. In North America the taxonomy
of the genus is difficult and therefore no unanimity of opinion
exists with respect to the most suitable taxonomic treatment.
Apomixis in the genus led to the formation of many distinct
polyploid races or clones, many of which were named as species by
turn of, to mid century taxonomists. Unfortunately, many of these
species were based on single collections from local populations
that have never been recollected. Most recent workers on the genus
have adopted a more conservative classification for this
group.
- Antennaria probably comprises 25-30 sexual diploid species and
several large polyploid agamic complexes derived from them.
Taxonomic differences are presumably due to the occurrence of
polyploidy, apomixis, and hybridization. In North America it has
been suggested that Antennaria is comprised of six large
polyploid complexes, namely A. howellii and A.
parlinii, mostly from eastern North America, and A.
alpina, A. media, A. parvifolia, and A.
rosea, mainly from western or arctic North America. In
attempting to delimit patterns of variation and thereby resolve
taxonomic confusion in the genus, the classification of taxa should
be derived not only from morphology and chromosome number
determinations (knowledge of cytogeographic distributions of taxa
is useful in determining the limits of distribution of
infraspecific variants, in constructing biogeographic histories of
species, and in testing hypotheses on the evolution of
infraspecific polyploidy), but also from experimental studies.
- Although most recent studies have focused on the use of
classical morphological analyses to ascertain phenetic
relationships within the genus, molecular techniques, specifically
random amplified polymorphic DNA (RAPD), is being used to examine
the phylogeny of the genus.
SEED ECOLOGY
- One of the more stable morphological characteristics of many
plant species is seed weight. Despite this cited stability,
variability in seed weight has been documented among species,
populations, cytotypes, individuals, and even within an
inflorescence.
- When variability in seed weight is recognized, it is generally
greater among those species in which flowering is determinate as
opposed to indeterminate. Presumably those species with an
indeterminate flowering pattern will more likely exhibit variation
which is attributable to environmental change as seed maturation
occurs over an extended portion of the growing season. Variation in
seed weight within an inflorescence indicates that those factors
responsible are likely nongenetic in origin, and that environmental
change during maturation is a probable cause. Others have argued
that seed weight is genetically controlled and thus subject to
evolutionary change.
- Many examples of seed polymorphism, that is, the production of
seeds with differing morphologies and or behaviors occur within the
Asteraceae, Brassicaceae, Chenopodiaceae, and Poaceae. The
production of dimorphic achenes has facilitated the evolution of
alternative strategies relative to dispersal, germination, and
dormancy.
- Some previous studies on members of the Asteraceae have
differentiated between germination in dimorphic ray and disc
achenes. Reduced dispersability and delayed germination are
characteristic of the outer (typically associated with the ligulate
ray floret) achenes, conversely, distance dispersal and quick
germination are characteristic of the central (typically associated
with the tubular disc floret) achenes.
- The inflorescence in Aster is actually a capitulescence
consisting of one, to possibly a thousand, capitula. These capitula
are typically differentiated into the centripetally maturing
peripheral, ligulate, imperfect pistillate ray florets and the
central, tubular, perfect disc florets. The achenes of Aster
pose yet a different question, that is, whether these apparently
monomorphic products of dimorphic florets exhibit comparable
tendencies to those of dimorphic achenes.
- Previous life history studies on Aster in which values
were reported for both achene (actually a cypsela) weight and
germination concurrently did not differentiate between achenes
produced from either ray or disc florets. Additionally, a
distinction was not made for germination per se, irrespective of
achene weight, for achenes produced by these two types of
florets.
- Although the florets per se of Aster are typically
morphologically different, ray and disc achenes are morphologically
indistinguishable. The senescence of floret parts (both ray floret
ligule and disc floret tube) in species of Aster prior to
complete achene maturation negate the possibility of reliable
separation of achenes based strictly on the position of a floret in
the capitulum. Inasmuch as these studies did recognize that our
inability to separate ray and disc achenes was a potential source
of variation, we concurrently did not know whether character
associations which were noted for the respective species were real
or incidental. Were character associations being obscured because
of our inability to separate ray achenes from disc achenes?
Dissatisfied with this possibility, a protocol was devised which
resolved this dilemma.
- The primary focus of this research is to determine whether ray
and disc achenes of Aster spp. differ relative to the
relationship of achene weight and its components of pericarp weight
and embryo weight to each other, to germination, and to the time
required to germinate (germination time). These results will be
used to compare evolutionary trends among those species which
perennate through herbaceous rhizomes, corms, or caudex.
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