Spermatopsida: The Seed Plants The most recent and most derived of the Spermatopsida comprise Phylum Anthophyta. These are the angiosperms, or Flowering Plants.

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?

...and so many others that it's clear these plants are monophyletic, since it's not likely that so many shared, derived characters would arise together via simple convergence.

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:

...and you should still be able to recognize and name all the basic parts.

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...

Placentation The placenta the point of attachment of the ovule to the ovulary wall. Placentation can be an important classification character, and in various plant taxa, placentation may be

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

...is said to be a complete flower. A flower that lacks one or more of these whorls is said to be an incomplete flower.

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.

  • spike - an elongate, unbranched, indeterminate inflorescence with sessile (i.e., lacking pedicels) flowers

  • spikelet - a small spike (found in grasses (Family Poaceae) and sedges (Family Cyperaceae)

  • raceme - an elongate, unbranched, indeterminate inflorescence with flowers on pedicels

  • panicle - a branching raceme

  • corymb - a flattened raceme (elongate pedicels at the margins of the inflorescence grow to reach the same level as the internal pedicels)

  • compound corymb - a branching corymb

  • umbel a flattened or rounded inflorescence with the pedicels radiating from a central, common point(may be determinate or indeterminate)

  • compound umbel - a branched umbel. Secondary umbels arise from the tips of the primary stalks

  • capitulum - (literally "head") - this inflorescence, characteristic of the Daisy Family (Family Asteraceae) is dense, vertically compressed and bears sessile flowers on a single receptacle. In many species, sterile ray flowers form a ring around a dense mass of central, fertile flowers. The entire inflorescence is subtended (held upon) an involucre (cluster of bracts) of phyllaries (small, scale-like bracts). May be determinate or indeterminate.

  • thyrse - main inflorescence is an indeterminate raceme; determinate cymes branch from the central raceme.

    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.

  • simple cyme, a.k.a. dichasium - two dichotomous lateral branches and pedicels of equal length

  • compound dichasium - a branched dichasium

  • compound cyme - a determinate thyrse

  • helicoid cyme, a.k.a. bostryx - a determinate cyme in which the branches develop only on one side due to abortion of opposing paired bud

  • cincinnus - a tight, modified helicoid cyme in which the pedicels are very short

  • scorpioid cyme, a.k.a. rhipidium - a zig-zagging, determinate cyme with alternate branches due to abortion of opposing paired buds at each rachis node

    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.

    Determining Evolutionary Relationships The earliest evolutionary botanists relied primarly on morphology and the fossil record to try and make sense of flowering plant relationships. But as we know, the fossil record is incomplete, and cannot yiel important molecular and cellular information that may be more relevant to determining actual common ancestry.

    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.

    ...suggesting that these characters could be primitive with respect to all angiosperms.

    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.

    Nymphaeaceae - Water Lilies and Their Relatives These plants returned to a watery existence some time in the late Cretaceous, essentially reproductively isolating themselves. They have remained relatively unchanged since that time.

    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.