BSC 314 Lecture Notes - Lecture 61: Magnoliids, Morphine, Dicotyledon
28 Jun 2018
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Phylum Anthophyta—The Flowering Plants
The Anthophyta, the angiosperms or flowering plants, is the largest and youngest
phylum of plants and the one whose members dominate the vegetation of the modern
world. The origin of the angiosperms is an enigma, but from all evidence they probably
arose sometime during the Late Jurassic or Early Cretaceous, but were first fossilized in
the Cretaceous. As they evolved over the ensuing millenia, they developed adaptations
that made them ever more successful in the competition for a place in the sun. At the
same time the angiosperms were diversifying, the terrestrial animals, too, were
diversifying and taking advantage of the new food source. The extraordinary success of
the angiosperms is not just that they have flowers—which certainly helps—but because
they have, as well, a combination of other structural, developmental, and ecological
features not found in their entirety in other groups.
The short list of characteristics of angiosperms includes:
Flowers, the means of reproduction
Ovules surrounded by two integuments.
Double fertilization, which leads to formation of polyploid endosperm tissue.
Simple microgametophytes and megagametophytes. The microgametophyte is a
three nucleate structure, the megagametophyte an eight nucleate one.‐ ‐
Stamens with two pairs of pollen sacs.
Sieve tubes and companion cells in the phloem, vessels in the xylem.
Evolution of flowers. With a spotty, incomplete fossil record of the early flowers, much
of the understanding of flower evolution is inferred from modern flowers. Taxonomists
for a century have defined angiosperm families on floral structure and separated
“primitive” from “advanced” features. In this assessment, early, primitive flower
characteristics are: an undifferentiated perianth with sepals and petals alike and
separate; an indefinite number of parts in each floral whorl; spiral attachment superior
ovaries; radial symmetry; and so forth.
Early carpels were leaf like and seeds were borne on the edges. In advanced flowers, ‐
the carpel is folded inward and the seeds are enclosed. Closed carpels have
differentiated stigmas, styles, and ovaries. The pollen does not land on the ovules
directly.
Pollination. Flowers and their pollinators coevolved; that is, two or more species act as
selective forces on one another and each undergoes evolutionary change. Early flowers
probably were wind pollinated, but the selective advantages of cross fertilization by ‐
animal pollinators must have been a powerful selective evolutionary force from the very
beginning.
Specializations to ensure cross fertilization and attract pollinators include: colors in ‐
wavelengths visible to the pollinators; nectaries placed so that access requires passage
across pollen sacs; odors; structural changes such as long corolla tubes and spurs filled
with nectar.
Dispersal. Concomitant with the changes to insure fertilization are those that insure
dispersal of the products of fertilization, such as the seeds and fruits. Fruits can be dry
or fleshy, remain closed or split open at maturity, have hooks or spines that attach to fur
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Document Summary
The anthophyta, the angiosperms or flowering plants, is the largest and youngest phylum of plants and the one whose members dominate the vegetation of the modern world. The origin of the angiosperms is an enigma, but from all evidence they probably arose sometime during the late jurassic or early cretaceous, but were first fossilized in the cretaceous. As they evolved over the ensuing millenia, they developed adaptations that made them ever more successful in the competition for a place in the sun. At the same time the angiosperms were diversifying, the terrestrial animals, too, were diversifying and taking advantage of the new food source. The extraordinary success of the angiosperms is not just that they have flowers which certainly helps but because they have, as well, a combination of other structural, developmental, and ecological features not found in their entirety in other groups. The short list of characteristics of angiosperms includes:
