Taxonomy of
Flowering Plants - LECTURE
NOTES
Hugh
D. Wilson
The Gymnosperms
Distinctive features (within the context of other vascular
plants):
1. similar to angiosperms in that an ovule is produced, but this
is not enclosed by tissue (such as the angiosperm carpel) -
'gymnosperm' = 'naked seed' (see overview
from Ohio State University - Hort 300).
2. Pollen grain (with microgametophyte within) directly contacts
the ovule to fertilize the egg - in angiosperms the microgametophyte
makes direct contact with the ovule after its emergence from the pollen
grain, BUT angiosperm pollen does not make direct contact with
the
ovule.
3. no double fertilization to produce endosperm
(although double fertilization has been documented in Ephedra
and Gnetum) - nutritive tissue for the embryo in gymnosperms is
haploid, megagametophytic.
4. absence of vessel elements (exception = Gnetophyta)
5. absence of companion cells in the phloem.
6. presence of a many-celled or many-nucleate
megagametophyte
7. presence of archegonia (as in pteridophytes,
except
in genera - Gnetum and Welwitschia)
8. mostly woody plants
As with the dicot subclass, Hamameliidae, the gymnosperms are a
small, diverse group (72 genera in fewer than 11 families, ca. 750
species) that forms, however, a dominant element of the flora
in many large parts of the planet's surface. These plants are
also economically
important, mostly as a timber resource, and poorly understood in terms
of
biological relationship.
These plants are often treated as a single unit (Division or phyllum
Pinophyta)
with three primary subunits treated as subdivisions. The
treatment offered here, which follows that of the Flora of North
America (FNA), elevates
these three elements to division rank and moves Ginkgo biloba
from subdivision Pinicae to a monotypic division.
Palm or fern-like plants, no vessels, motile sperm, usually dioecious,
seeds born on MEGASPOROPHYLLS, also MICROSPOROPHYLLS, both usually born
in STROBILI. None native to Texas, but several cultivated. An archaic
group (Triassic to present) now represented by 3 families: Cycad images
are available from the University
of
Wisconsin (Madison) Department of Botany, and the Department
of Botany at the University of Hawaii. See also: The
Cycad Pages from the Royal
Botanic Gardens Sydney, Australia and the Gymnosperm
Database.
Cycadaceae
(monotypic - 47 species)
Stangeriaceae
(2 genera, 4 species as treated in your text - also treated as
monotypic)
Zamiaceae
(8 genera, 164 species - 1 in the FNA)
Trichopityaceae (extinct) and Ginkgoaceae
with at least six extinct genera and a single extant species (Ginkgo
biloba) which is native to China and cultivated in urban areas
(resists pollution) throughout the world. Apparently identical fossils
that are 200 million years old (Mabberley, 1993) but now known only
from cultivation
and probably saved from extinction via cultivation - broad leaves,
motile
sperm. Ginkgo biloba images
are available from the University of Wisconsin (Madison) Department of
Botany, and information
on
the species can be obtained from the Gymnosperm database
(Department
of Botany, Rheinische Friedrich-Wilhelms-Universität Bonn,
Germany).
This division includes most of our extant gymnosperms in 6 families
with 52 genera and ca. 614 species. We have two genera of the Pinaceae
in
Texas (Pinus (8) and Pseudotsuga (1)). The North
American
flora (at least that portion covered by the FNA) includes 6 genera and
66
species. Conifer images
are available from the University of Wisconsin (Madison) Department of
Botany; a detailed (species descriptions) overview of trees of the
Pacific Northwest is provided by Oregon State University; and a
nice presentation of the ancient Bristle
Cone Pine has been created by Leonard Miller.
order Taxales
Taxaceae
(Yews) - five genera, with 17-20 species in mostly the northern
hemisphere - ovule surounded by green or red fleshy aril (an
appendage or
outgrowth from the hilum or funiculus that forms a
baccate
(berry-like but not a berry) pulpy or fleshy seed
covering.
See images of Taxus
from the University of Wisconsin.
order Pinales
Pinaceae
- 10 genera, ca. 200 species mostly in the northern hemisphere
with 6 genera (Pinus - pine, Larix - larch, Picea
- spruce, Tsuga - hemlock, Abies - fir, and Pseudotsuga
- Douglas-fir) and 66 species in the North American Flora. See
Fig. 60.
Cupressaceae
(including the Taxodiaceae) - 25-30 genera, ca. 110-130 species
with 30 species in the FNA and 3 genera (Taxodium, Cupressus,
and Juniperus) with 11 species in Texas. Includes Sequoia
sempervirens (coast Redwood) and Sequoiadendron giganteum
(Sierra
Redwood), the tallest and most massive living organisms. See our
local Taxodium.
Araucariaceae
- (Norfolk Island Pine or Araucaria
Family)
- 2 genera, 39 species -
Once (Jurassic and Cretaceous periods) of worldwide distribution, now
restricted to the Southern Hemisphere. "Living fossil" (The Wollemi Pine - New South
Wales, Australia) discovered in 1994, probably a new genus - only ca.
100 plants known. See See images from the Department
of Botany at the University of Hawaii
Podocarpaceae
- 13-17 genera with ca. 170 species - elements form major forests in
some parts of the family range - Southern Hemisphere. See images
from
the Department
of Botany at the University of Hawaii, and our
local podocarp.
3 orders - each with a single famly that includes a single genus -
with ca. 90 species - unusual plants that show, relative to other
gymnosperm
groups, structural similarities to the flowering plants.
order Ephedrales - shrubs with jointed stems and
reduced leaves, vessels, and double fertilization (no endosperm
produced)
- Ephedra
- ca. 60 species of the Northern Hemisphere and South
America, 12 species in the FNA and 6 species in Texas. See Ephedra
torreyana and blurb from commercial producers.
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