| Class:
Magnoliopsida (Dicotyledons) |
|
| Asteridae |
Magnolidae |
| Asteraceae
(Sunflower) |
Berberidaceae
(Barberry) |
| Caprifoliaceae
(Honeysuckle) |
Rosidae |
| Oleaceae
(Olive) |
Aceraceae
(Maple) |
| Polemoniaceae
(Phlox) |
Anacardiaceae
(Sumac) |
| Caryophyllidae |
Fabaceae
[Leguminosae] (Pea) |
| Chenopodiaceae
(Goosefoot) |
Hydrangeaceae
(Hydrangea) |
| Dilleniidae |
Onagraceae
(Evening Primrose) |
| Ericaceae
(Heath) |
Rosaceae
(Rose) |
| Salicaceae
(Willow) |
Saxifragaceae
(Saxifrage) |
| Hamamelidae |
|
| Betulaceae
(Birch) |
|
| Class:
Liliopsida |
|
| Poaceae
[Gramineae] (Grass) |
Cyperaceae
(Sedge) |
Division:
Magnoliophyta
The
division Magnoliophyta (Anthophyta) , the flowering plants, are believed to
be the most recently evolved and the most successful plants on earth. They
compose the largest groups of plants with vascular tissue (water conducting
tissue composed of xylem and phloem) in number of individuals and in diversity
as shown by the number of genera and species. There are approximately 300,000
species of flowering plants grouped into approximately 12,000 genera. Flowering
plants include trees, shrubs, herbs, vines, floating plants, epiphytes, and
even parasites which do not have chlorophyl. They can be found in almost all
habitats–xeric, mesic, and hydric. They comprise the dominant portion
of the vegetation most areas. Their life cycles include annuals, biennials,
and perennials. They may be evergreen or deciduous. The perennials include
woody types with secondary growth such as trees, shrubs, and vines. Perennial
herbaceous types without secondary growth survive dormancy periods such as
dry seasons or winter by corms, bulbs, rhizomes, or other underground organs
such a woody caudex.
The following is an abbreviated summary of flowering plant anatomy. For more
details, studying any general botany or plant anatomy or morphology book is
suggested.
A flowering plant normally consists of roots, stems, leaves, and reproductive
parts. It begins its life as an embryo within the seed. The embryo has a terminal
bud at one end and a primary root or radicle at the opposite end. Seed leaves
(cotyledons) are attached at a midpoint which divides the stem from the root.
The area below the attachment point of the cotyledons is called the hypocotyl
and the region above is termed the epicotyll. Roots which branch from the
radicle are called secondary roots. Roots which arise from anywhere else on
the plant, usually from somewhere on the stem, are called adventitious roots.
The leaves of flowering plants are termed macrophyllous (macro = large, phyllous
= leaves). However they vary greatly in size. Palm leaves my be several feet
in length while those of cacti and spurges may be almost microscopic. Stems
are roughly divided into regions called nodes and internodes. Leaves arise
from nodes . If only one leaf arises from each node, it is referred to as
alternate leaf arrangement. They appear to be spiral up the stem. If two leaves
arise from a node, the condition is referred to as opposite leaf arrangement.
If three or more leaves arise from the node, it is referred to as whorled
leaf arrangement. The angle formed by the leaf stalk (petiole) is referred
to as the leaf axil. In this axil, there is usually a bud which is referred
to as the axillary or lateral bud. It normally has the potential to become
either a branch or an inflorescence or rarely a spine. The flat portion of
a leaf is referred to as the blade. If it is undivided, it is a simple leaf.
Its edges are called the leaf margin which may be toothed (dentate), serrate,
or lobed. If the blade is divided all the way to midrib, it is referred to
as a compound leaf. There are two types of compound leaves. If the divisions
come off the midvein as the divisions come off a feather, the leaf is referred
to as pinnately compound. If the divisions all appear to come off one point
at the tip of the petiole radiating outward, it is a palmately compound leaf.
Some plants have two lateral appendages attached to the stem at the base of
the petiole. These are stipules. In some families such as in some of the spurge
family members or some pea family members, they may be spines rather than
leaf-like.
The veins in leaves may be parallel as in the Liliopsida or they may form
a network as in the Magnoliopsida. Rarely they may be dicotymously branched.
A cross section of a leaf reveals epidermis on both the adaxial and abaxial
surfaces. Between these two layers lies mesophyll which is usually divided
into two regions. The orderly arranged portion usually adaxial is palisade
mesophyll while the less orderly cells are called spongy mesophyll. Chlorophyll
is located in the mesophyll, but not in the epidermis. Openings in the epidermis
which allows for gaseous exchange including loss of water vapor are called
stomata. They have specialized cells which open or close called guard cells.
The veins or vascular bundles contain both xylem and phloem. Sometimes the
xylem and phloem are surrounded by specialized, often thick walled cells called
the bundle sheath. Leaves do not just break off anywhere, but there is a special
region which breaks easily called the abscission layer. This also is so constructed
that it prevents loss of fluids.
The stems of flowering plants vary. They may be erect, decumbent, prostrate,
or climbing. Stolons are prostrate on the substrate surface. Rhizomes are
horizontal below the ground. Underground stems also include tubers, bulbs
and corms. Underground parts may be woody having secondary growth or soft
having no secondary growth. Xylem vessels are found in all but a few (100
or so) species. These contain no cytoplasm when they function to conduct water
from the roots upward in the stem. The phloem contains companion cells adjacent
to the sieve cells. Sieve cells contain cytoplasm, but have no nucleus. Stems
branch by the growth of the axillary buds which are located on the stem surface.
In the dicots (Magnoliopsida) the emergent radicle my persist as a deep-growing
taproot. In many monocots (Liliopsida) such as grasses, the radicle may stop
growing and the subsequent root system is composed entirely of adventitious
roots. Roots do not have nodes and internodes as stems do. Roots branch from
the pericycle layer at any location, not from a surface located axillary bud
as in stem. To differentiate between rhizomes and roots, one can find nodes
from which scale-like remnants of arise. In their axils, the axillary buds
my give rise to vertical stems. Adventitious roots also come from the nodes.
The nodes are separated from each other by internodes just as in above ground
stems. The branches of roots appear to arise randomly from any location.
Class:
Magnoliopsida
(Dicotyledons)
The
Class:
Liliopsida
The