This clade has undergone a great deal of revision with molecular data, and the taxon is now divided very differently from its original classification. Let's take a quick look at the Current Classification of the Anthophytes.
Angiosperms are the most diverse and successful plants, numbering anywhere from 300,000-450,000 species, with many yet to be scientifically named and described. Their morphological diversity is unmatched among living things, with some species of Eucalyptus exceeding 100 meters in height, and others being nearly microscopic.
Anthophytes can be herbaceous or woody, upright or vines, annuals or perennials, shrubs or trees...you name it. Flowering plants have been the dominant life form on earth for over 100 million years.
What synapomorphies set angiosperms apart from other plant phyla?
Anthophytes were once divided into two main groups, "dicots" and "monocots," but more recent data reveal that this was an artificial separation based mainly on the high degree of derived character states seen in the monocots. As you can see from the phylogenetic tree of anthophytes we viewed before, the "dicots" are actually not all derived from a single ancestor.
The Flower: Vocabulary-o-Rama! We already have seen the basic anatomy of a typical flower:
Like a pine needle fascicle, a flower is actually a determinate shoot that terminates in leaves. But these leaves are all highly specialized for reproductive, and even the sterile portions (stamens, petals) may assist in this regard.
Flower Anatomy Be sure you remember the meaning and significance of...
Parts Gone Missing: Complete and Incomplete, Perfect and Imperfect Flowers A flower can have four types of specialized leaf whorls, the (1) calyx and (2) corolla (sterile) as well as the (3) androecium (microsporophylls) and (4) gynoecium (megasporophylls). Most flowers have all four, but in some cases, one or more of the whorls has been secondarily lost. A flower that has
A loss of the reproductive whorls has special terminology. A flower with both stamens and pistil(s) is said to be a perfect flower, whereas one missing either of those is said to be an imperfect flower. Recall that if a single plant has only male or only female flowers, then that species is dioecious, but if a single plant has either separate male and female flowers or perfect flowers, that species is monoecious.
(A special note about mangos and avocados...)
Inflorescences Flowers may be borne singly, on a peduncle, or in a cluster called an inflorescence. The tiny stalk of an individual flower in an inflorescence is called a pedicel.
Inflorescence morphology is another useful classification character, and of course we have a massive vocabulary to describe them!
I. Indeterminate Inflorescences
An indeterminate inflorescence has new buds growing at the apex while mature flowers appear on lower pedicels. Buds open first from the base of the inflorescence.
II. Determinate Inflorescences
A determinate inflorescence has new buds growing at the base while mature flowers appear on upper pedicels. Buds open first at the top of the inflorescence.
Ovulary Position And it just gets worse. The position of the ovulary attachment--with respect to the other whorls--is another way to classify the plant you're trying to identify.
As we'll see, this will affect the morphology of the fruit that develops from the ovulary and associated structures.
The Life Cycle Once again, the alternation of generations appears, but now the female gametophyte reaches her most reduced form, lacking even archegonia.
A closer look at the female gametophyte:
And from this, comes the seed, whom you've already met.
Anthophyta: Evolutionary Wonders The early Cretaceous saw the first appearance of flowering plants in the fossil record. By the mid Cretaceous, about 90 million years ago, flowering plants were the dominant life form on earth. This is a tremendously quick rise to dominance, geologically speaking. What is it that made the Anthophytes so successful? There are several hypothetical explanations, all of which probably contributed.
To this day, morphology is still a major tool in plant cladistics, though more and more molecular data are helping to clarify relationships. Let's once again remind ourselves of the current (and subject to revision!) Classification of the Anthophyta.
Synapomorphies that link the angiosperms are
(Meaning that these characters were present in the common ancestor of all angiosperms.)
Recall that the old phylogeny divided plants into "dicots" and "monocots." We now know that there are some plants that are neither (as long as you are following cladistic classification methods that allow only monophyletic taxa).
One symplesiomorphy shared by some anthophytes with cycads and ginkgos is pollen with a single aperture through which sperm exit. Hence, single-aperture pollen is a primitive character with respect to anthophytes. It is found in all anthophytes except the Eudicots, which have pollen with three apertures, a synapomorphy that links all the eudicots and separates them from all other anthophytes.
Let's Meet the Anthophytes... The most primitive flowering plants were once called "dicots," but we now know that this term is not monophyletic. Several groups have been removed and placed in separate taxa.
The earliest known angiosperm, a fossil discovered in China, is the appropriately named Archaefructus.
Amborellaceae - A Unique Living Fossil The living anthophytes that retain the most archaic characters are found in New Caledonia. Of these, the most primitive is Amborella trichopoda, the only species in the most primitive anthophyte family, Amborellaceae. It's a short, evergreen shurb that has undifferentiated perianth parts (no distinct petals or sepals). It's dioecious, with separate sexes, and having relatively primitive sporophylls. It produces small, red fruits (drupes, which you'll meet later) and it's seeds have resin deposits reminiscent of the more primitive seed plants.
Let's remind ourselves of where we are on the Tree of Life.
More details on the Nymphaeaceae.
Magnoliidae Once believed to be the most primitive of all flowering plants, the magnolias and their allies are now accorded separate status. There are several commercially important groups, such as the Lauraceae (Laurel Family), the Piperaceae (Piper Family), and the Magnoliaceae.
Until 1991, most botanists believed that the earliest flowers resembled those of the magnolia, with large, numerous, spirally arranged (not whorled) petals. We now know that Archaefructus preceded magnolia-like flowers by 10-20 million years. Showy flowers came later!
Monocots The monocots are probably the most distinctive and easily recognized of all angiosperms. they have
These include many economically important plants, including all the grasses (corn, wheat, oats, rice, etc.), palms, sedges, orchids, lilies, etc.
The monocots have traditionally been paired with the eudicots as the two major lineages of flowering plants, and may be sister taxon to them. This has yet to be resolved.
Eudicots The term "eudicot" was first coined by J. A. Doyle and C. L. Hotton in 1991. Things have never been the same.
This group contains the vast majority of flowering plant families, though many relationships within this taxon remain unresolved. A discussion of all the eudicots could span many semesters. So we must content ourselves with discussing the diversity of their most defining characters: flowers and fruit.