I was enjoying some citrus the other day when I got to thinking about these peculiar fruits. They are some of my favorites yet I know very little about their development. What is a citrus fruit exactly and why are they so juicy?

To start with, citrus fruits are produced by members of the citrus or rue family - Rutaceae. Not all members of this family produce them either. Technically speaking, the oranges, lemons, limes (etc.) we eat are specialized berries called "hesperidia." They are characterized by their tough rind and juicy interior.

Following fertilization, the ovary of each flower begins to swell. On the outside of the swelling fruit you find the rind or “pericarp.” The pericarp itself has a few layers associated with it but this is where the oil-filled pits are located. Anyone that has ever squeezed an orange peel has seen these pits spurt their contents.

Citrus australasica, the Australian finger lime or caviar lime. Photo by Amada44 licensed under CC BY-SA 3.0

Inward from the pericarp are a series of segments, which are the carpels. The individual carpels are the reason why oranges can be so easily segmented. Inside each carpel is a locule. These are small cavities where the seeds are housed. Lining the walls of these loculi are tiny hairs that, as the fruit matures, gradually fill with juices.

These juice-filled hairs makeup the pulp of a citrus fruit. Look closely and you can see that they are indeed individual compartments. This not only provides some nutrients to the developing seeds, it also provides a meal for potential seed dispersers, thus increasing the chances of successful recruitment away from the parent tree.

From a quick snack I spiraled into a world of new information. It is amazing what you can learn from simple questions. As a botanically oriented person, every meal offers a sea of discovery!

Photo Credit: [1] [2]

Further Reading: [1]

Photo by Ryan Bushby licensed under CC BY 2.5

Love them or hate them, one must respect the fiery chili pepper. If you're like me then the addition of these spicy fruits can greatly enhance the culinary experience. For others, spice can be a nightmare. Peppers are so commonplace throughout many cultures of the world that it is easy to overlook them. As a plant fanatic, even the simple act of cooking dinner opens the door to so many interesting questions. What is a pepper? Where do they come from? And why are some so spicy?

Peppers evolved in the Americas. The genus to which they belong, Capsicum, is comprised of somewhere around 27 species. Of these, five have been domesticated. They have no relation whatsoever to black pepper (Piper nigrum). Instead, the chili peppers are relatives of tomatoes, potatoes, and eggplants - family Solanaceae.

The fruit that they produce is actually a type of berry. In the wild, Capsicum fruits are much smaller than the ones we buy at the farmers market or grocery store. Centuries of domestication has created such gaudy monsters. The spicy effect one experiences when biting into a pepper is the result of a chemical called capsaicin. It is mainly produced in the placental tissues and the internal membranes. It is in its highest concentrations in the white pith that surrounds the seeds.

As with any fruit, the main goal is seed dispersal. Why then would the plant arm its fruits with fiery capsaicin? The answer to this riddle lies in their wild relatives. As mentioned, the fruits of wild peppers are much smaller in nature. When ripe, they turn bright shades of reds, yellows, and oranges. Their small size and bright coloration are vivid sign posts for their main seed dispersersal agents - birds.

As it turns out, birds are not sensitive to capsaicin. Mammals and insects are, however, and that is a fact not lost on the plants. Capsaicin is there to deter such critters from feeding on the fruits and wasting hard earned reproductive efforts. As such, the well defended fruits can sit on the plant until they are ripe enough for birds to take them away, spreading seeds via their nutrient rich droppings.

It may be obvious at this point that the mammal-deterring properties of Capsicum have been no use on humans. Many of us enjoy a dash of spice in our meals and some people even see it as a challenge. We have bred peppers that are walking a thin line between spicy and dangerous. All of this has been done to the benefit of the five domesticated species, which today enjoy a nearly global distribution. Take this as some food for thought the next time you are prepping a spicy meal.

Photo Credits: Ryan Bushby, André Karwath, and Eric Hunt - Wikimedia Commons

Further Reading:
http://link.springer.com/article/10.1007%2FBF00994601

http://www.jstor.org/stable/4163197…

http://www.press.uchicago.edu/ucp/journals/journal/ijps.html