flowers

Have you ever wondered through a garden or a woodland and seen a lovely flower and wondered what it was? How do you find out? First you need to know some basic information about flowers.

From their first appearance on earth at least 130 million years ago, flowering plants (angiosperms) have evolved a diversity of colors, shapes and sizes. Small differences in size, shape and placement of reproductive parts developed in response to environmental factors and simple genetic changes. While some flowers can self pollinate, most require the wind, insects, birds or other animals to help with reproduction. Design differences can offer be associated with pollinators.

Plants are often grouped into families based on similarities in their anatomy. Flower structure and the characteristic arrangement of those flowers on a stem (the inflorescence) can provide useful clues to plant identity and can help to establish a potential relationship to a particular group of plants that share particular attributes.

Before we can learn to identify or group flowering plants, we need to learn some basic terminology, so lets have a look at a few flowers from my garden.

More about flower parts and form
	In this photograph of a geranium flower are five green sepals that sit behind and alternate with five pink petals. Together the sepals for the calyx; together the petals for the corolla. The calyx and corolla form the perianth. This flower is actinomorphic. This means that the flower has a radial symmetry — it can be divided into two equal halves by two or more planes (5 here).
	Flowers that can be divided into equal halves along only one line have bilaterally symmetrical and are termed zygomorphic. The flowers of the iris and the snapdragon are zygomorphic. Most members of the legume family (Fabaceae ) and all members of the subfamily Faboideae (or Papilionoideae) like this Red Bud (Cercis canadensis) are zygomorphic. Most Lamiales (think lamiums) tend to be zygomorphic.
	Although this dandelion looks actinomorphic, it is actually made up of zygomorphic florets.
	Some flowers have showy sterile bracts (modified leaves) in addition to or in place of the perianth. Lavandula stoechas (left) has a pink bracts at the top of the flower spike to attract pollinators. Flowering dogwood, bougainvilleas, poinsettias all have colourful bracts.
	Connate parts are similar parts fused together. Connation can affect each whorl, sepals, petals, stamens, and/or carpels. In the Berginia cordifolia, pictured right you can see the sepals are fused basally. The tubular perianth of muscari (left) is due to connate tepals. When the petals are connate, at least at their base, the flower is sympetalous. (syn- or sym- means united).

With at least a quarter million species of angiosperms, we need a system to narrow down the possibilities. A useful first step is to determine if the plant belongs to one of two broadly defined groups, the monocots (Monocotyledoneae) or the dicots (Dicotyledoneae). While this is an old sorting system and not without controversy, it can provide useful clues to a plants identity. Once the plant has been assigned to a particular group, then it can be sorted into a particular family and genus. From there, the particular species can be teased out from the finer details.

Less than one quarter of angiosperms are monocots. Monocots include such diverse plants as orchids (family Orchidaceae), grasses and sedges (families Poaceae and Cyperaceae), lilies and daffodils (Liliaceae and Amaryllidaceae), onions (Alliaceae) and palms (Arecaceae). In common, these plants have only one cotyledon (mono - cotyledon - this is the first leaf that emerges from the seed). Typically, they are herbaceous (no woody tissue) with scattered vascular bundles. They have parallel leaf venation and flower parts come in multiples of three: e.g. three petals, six stamen etc. The roots are typically fibrous and adventitious roots emerging at nodes in the stem as the embryonic root (radicle) is aborted.

Dicots are a much larger diverse group. This group includes the sunflower family (Asteraceae), the legume family (Fabaceae), the geranium family (Geraniaceae) the rose family (Rosaceae) the carrot or parsley (Apiaceae) family etc. As you would imagine dicots are defined by having two cotyledons (think of a bean plant sprouting). Generally dicots have more complex vein structure (veins that are netted or reticulated). Roots emerge from the seed, and are a continuation of the radicle. Typically, their floral parts occur in multiples of four or five. They include woody plants (e.g. trees) and have vascular bundles in a ring arrangement.

Carpel Anatomy
The carpel (if single) or carpels (if fused) comprise the pistil of the flower. A flower with two or more fused carpels (called a ''compound ovary'' or ''compound pistil'') is termed ''syncarpous''. However, if the gynoecium consists of more than one distinct carpel, it will have more than one ''pistil'' and is then termed ''apocarpous''. ''Apocarpous'' also pertains to any flower with a single carpel. (Wiki definition)
	Apocarpus The petals have been removed from this magnolia blossom (far left) or the Anemone sylvestris to reveal the stamens and compound pistil made up of many distinct carpels. Click on the thumbnails for a closer look.
	Syncarpous While it may not be immediately apparent, the pistil of the tulip is made up of three fused carpels as the three-lobed stigma suggests. Click on this thumbnail for a closer look. Some families that exhibit syncarpy: Papaveraceae, Cruciferae, Caryophyllaceae, Violaceae (see What Plant Family is It?)