For centuries botanists have attempted to sort and categorize plants. Flowering plants have held a particular fascination. As early as 1682, Englishman John Ray suggested grouping plants in two categories--Dicotyledons and Monocotyledons--in his work "Methodus Plantarum Nova." A century later, a French botanist, Antoine Laurent de Jussieu, expanded on this work. In the monocot/dicot system, plants are assigned to one of the the two categories according to the presence or absence of a number of factors, including characteristics of seeds, roots, growth form, pollen configuration, vascular systems, leaf configuration and flower configuration. All monocots and dicots bear flowers, though some flower very rarely or have flowers that are so insignificant as to be unnoticeable.
Hidden within the seeds of flowering plants are "seed leaves" or cotyledons, that are produced by each seed's embryo. These seed leaves absorb nutrients until the plant forms true leaves and can absorb sustenance through photosynthesis. The defining characteristic of a monocot is its single seed leaf. In general, monocots are also characterized by fibrous or fleshy roots, linear leaves with veins that run parallel to the length of the leaf, flower parts that occur in multiples of three, a vascular system composed of scattered bundles, pollen with only one pore and an herbaceous (rather than a tree-like) growth form.
Examples of monocots, which accounts for about 25 percent of all flowering plants, include grasses, orchids, lilies and irises.
Dicots have two seed leaves in each seed. These plants are also characterized by strong taproots, cylindrical vascular bundles that ring the interior of the stems, pollen grains with three pores, relatively broad leaves veined in a net-like configuration, woody or herbaceous growth forms and flowers with parts in multiples of fours or fives.
The majority of flowering plants, including geraniums, roses and daisies, are dicots.
Since monocots and dicots share a common ancestry, there are some plants that exhibit characteristics of both monocots and dicots. Waterlilies appear to have a single cotyledon, but also feature the reticulate or netted leaf vein configuration of a dicot. Palms, which are monocots, appear to have the woody trunks that are more characteristic of dicots. This is because the "trunks" are actually composed of overlapping leaf bases.