April 12, 2012
Diversity among the Rosaceae Family
Many of us are familiar with the typical garden rose, but these are mainly ornamental roses. There is so much more in the Rosaceae family, like different types of trees and shrubs covered in many colors of flowers, although blue is mainly excluded from the rose color scheme. The diversity throughout the Rosaceae family is great. From the type of plant, whether it be a tree, shrub, or perennial herb, to the style of leaves, the differences of thorns and prickles, and their different flowers.
There are quite a few different types of plants in this family such as, trees, shrubs, annual or perennial herbs, a few climbers like vines, but no aquatic plants. These plants can be armed with branch thorns or surface prickles, but some, like the Amelanchier utahensis, the Utah serviceberry are not. There is a great difference between the different types of defensive additions, known as thorns, prickles, and spines. Only thorns and prickles are found among the Rosaceae family. These defensive additions are deferentiated by what part of the plant they are adapted from. Thorns are modified branches and stems, while spines are modifications of an entire leaf. Prickles are different all together because they are not modifications of leaves or branches, but grow out of the epidermis or cortex of the plant. Prickles are mainly just on roses and raspberries.
The flowers are usually radially symmetrical with five sepals, five petals that attach to a cup-like structure, with numerous stamens, and either a compound ovary or several simple ovaries.
The leaves are typically simple and alternate, but there are always exceptions. When there are compound leaflets they tend to be opposite instead of alternate. The leaves tend to be serrated and choppy along the edges.
There are three subfamilies in the Rosaceae family, they are Rosoideae, Maloideae, and Dryadoideae. Those in the Rosoideae subfamily are mainly aggregate fruits made up of achenes or drupelets, where the main portion of the fleshy fruit is made of receptacle tissue. This subfamily contains roses, blackberries, raspberries, strawberries, and more. Maloideae usually have five capsules (aka. Cores) in a fleshy or stony endocarp, with a fleshy mesocarp, otherwise called a pome. The third subfamily, Dryadoideae is traditionally hairy achenes.
The fruits of the Rosaceae family are achenes, pomes, drupes, or aggregates of drupes. Many of the fruits in the Rosaceae family are fleshy and red, purple or yellow colored. Most of these are in the category of fleshy fruits, except for achenes which like strawberries look like they are fleshy fruits, but are not. Achenes are in the category of dry fruits. Dry fruits are known for having a dry mesocarp when they have reached maturity and are ready for seed dispersal. Achenes are also among those indehiscent fruits because they do not split apart to spread their seeds.
Pomes are fruits that come mainly from non-ovarian tissue such as, the floral tube or receptacle. Some of these types of fruits are apples and pears. With a papery or leathery endocarp surrounding their seeds and in those like apples the core is made up of ovarian tissue and some of the surrounding tissues of the flower. Pomes are considered an accessory fruit because of the amount of additional tissue of the fruit that comes from parts of the plant other than the ovary. Typically fruits like these come from epigynous ovaries, ovaries that are inferior to the remainder of the flower.
Drupes are fleshy fruits with a single seed enclosed in a stony endocarp, otherwise known as a pit. These normally arise from flowers that are hypogynous, having superior ovaries. These types are also called stone fruits, and contain fruits such as apricots, cherries, peaches, plums, olives, and almonds. Most of these are in the Prunus genus within the Rosaceae family, all of these mentioned except for olives.
Aggregate fruits come from a single flower that holds multiple pistils. Each of these pistils develops into miniature drupes and remains in a cluster remaining on the receptacle. Some aggregate fruits include raspberries, blackberries, and strawberries.
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