A Visual Classification of Assorted Citrus Fruit.

For the purposes of this visual classification, the subjects are most easily divided into two broad categories, then further into three subcategories. In the broadest, each of the four fruiting bodies is one of two colors, either orange or yellow, and one of two shapes, elongated spheroid or compressed spheroid. Seeing as these divisions are compound, in that all the yellow fruiting bodies are elongated whereas the only orange fruit is compressed; the fruits can be separated into distinct groups by these major characteristics. From here on, each will be referred to by their group name, either yellow group or orange group.

Within the yellow group, certain similarities are shared in addition to their common color and form. While all are elongate, all also possess distinct rounded protrusions at each end of their major axis. Inside each of these protrusions is a small attachment scar. For each fruiting body, one scar is more pronounced, while the other is subtler. The nature of these scars points towards the conclusion that these fruiting bodies grow on a tree or woody shrub of some sort, as they appear wholly different than the types of attachment scars found on fruiting bodies that grow on vines or non-woody shrubs.

Inside the yellow group, the main division falls on the fruits’ surface texture and size. The two largest specimens have a skin that is extensively crenellated and wrinkled over the entire surface of the fruit. The smaller specimen is smooth save an even scattering of small pore-like dimples and extremely shiny and slick to the touch. This difference in external covering implies a different set of environmental conditions in the growing region of the rough and smooth fruiting bodies. Given its smooth texture and waxy appearance, the smaller of the fruits would appear to hearken from an arid climate. This waxy looking coating retains water and keeps the fruit from becoming desiccated via transpiration in the heat of the day. A similar waxy coating can be found on the leaves of several other succulent plants that thrive in the dryness of deserts, reinforcing this conclusion. Conversely, the larger rougher fruits would appear to be native to a very moist environment. The rough, porous, highly textured surfaces of the fruit provide a gratuitous amount of surface area from which transpiration can occur. Thus, the fruiting body aids in the circulation and expulsion of excess water to keep the sap of their plant circulating and providing nutrients for their continued growth. In extremely wet environments, nutrients are often much diluted, so this aid to increased sap flow into the fruiting bodies is essential for proper growth.

The structure of the attachment scars on the three yellow fruits serves to reinforce the above conclusions. On each of the large wrinkled fruits, the major attachment scar is broad and multi-pored. This shows that the stem attaching each fruit to its plant was sturdy and had many vessels to transport sap into the fruit. Additionally, the thick stem provides enhanced attachment support for the fruit in the face of the torrential rains it faced in its native climate. The smaller waxy fruit’s attachment scar is much thinner and also waxy. In an arid climate smaller surface area of a plant’s stems allows less moisture to escape via transpiration. The thick stems of the larger fruit are not required, as the waxy smaller fruit does not need to withstand the buffeting of heavy rains.

Switching to the wholly separate category of fruiting bodies, the orange fruit shares a few similarities with its yellow cousins. Like the others, it has scars at each end, however since it is compressed as opposed to the elongate yellow fruit, each of the scars lies on its minor axis. Its skin is midway between that of each extreme of the yellow fruit. While it is not wrinkled like the wet-climate fruit, neither is it waxy like the arid-climate fruit. This leads to the conclusion that the orange fruit is from a more temperate region with average rainfall. The extreme transpiration-enhancing qualities of a wrinkled skin are not required, nor are the moisture retaining qualities of a thick waxy coating.

The orange fruit’s attachment scar closely resembles that of the larger yellow fruits’ but in size falls between that of the larger and smaller of the yellow fruits. This further reinforces the conclusion that the fruit’s plant grows in an environment with average rainfall. As was concluded with the yellow fruits, the orange fruit appears to grow on a tree or woody shrub as well.

The final notable quality of the orange fruit is perplexing, and perhaps cause for further study. As opposed to the minor attachment scars of the yellow fruits, which clearly show the location of the flowering body, the minor scar on the orange fruit takes the appearance of a recessed spheroid beneath the surface. This spheroid can be seen through a circular excision that makes up the minor scar. It is possible that the fruit in its growth overtakes part of the flowering body, which is then incorporated bodily into the distal end of the fruit. This would imply that the flower itself is quite small, and perhaps recessed in some way into its stem. Whereas the yellow fruits’ flower attachment scars appear normal and reflect a common flower, perhaps this recessed unusual scar on the orange fruit reflects a specialized flower. As common flowers are most often pollinated either by wind or winged insects, perhaps the specialized flowers of the orange fruit indicate a climate without a sufficient winged pollinator, or some hindrance to airborne pollination. In this case, the flowers could be smaller and recessed to entice ants or other small crawling insects into the flower body to aid in the pollination of the plant.