dehiscent fruits

As I mentioned earlier, there are a few more types of dry fruits... I'm going to go into nine in total. Not all at once though, since we break this larger group up a little bit based one whether the fruits are dehiscent or indehiscent (again, based on whether or not they break open to release the seeds)

Asclepias (Milkweed), a dry fruit, opening to release seeds

Ok, it's actually possible that I didn't take that photo. It was clearly taken in the North End at the Greenway, but I don't remember taking it, and it is dated 2009 which is before I really started taking photos there. Then again I do like milkweeds so it might have been me. If it wasn't me, it was almost certainly Tom Smarr who took it.
Regardless, I think this photo is ideal for getting a feel as to what a dry fruit is and how it differs from a wet fruit. Think back to the diagrams of the wet fruits: you can clearly see the pericarp (comprised of the exo, meso, and endocarp) is much thinner on the milkweed, most noteably lacking that characteristic layer of fleshy mesocarp we saw in all the wet fruits. Though the pericarp still covers and contains the seeds in a dry fruit, it is not attached to them nor does it hold them in place, leaving the seeds to freely disperse as soon as the fruit opens.

The peanut, a legume. Taken from Wikipedia's Peanut entry
as I have no peanuts in the house. .. and even if I did
there would be no shells. Pericarp just gets in the way.

If you're not quite seeing the difference yet, contrast in your mind a banana and a peanut. If you cut a banana in half, the seeds still for the most part remain in the banana, stuck in and attached to that layer of fleshy mesocarp. On the other hand, if you split a peanut shell, the two seeds (peanuts) will fall right out. there's nothing there to hold them to the shell. Banana's a wet fruit, the peanut shell is a dry fruit.

The Milkweed and Peanut are both examples of simple dry fruits. Simple, in this case, means the fruit is the result of only one ovary maturing, and that two or more have not combined to form an aggregate fruit.
The Milkweed fruit is a follicle, a simple dry fruit that splits down one side to release the seeds. The peanut is a legume, a simple dry fruit that splits along both sides when releasing the seeds.

Now. though you probably believe me that the peanut fruit splits down both sides, you might be scratching your head as to why I'm saying the milkweed fruit splits down one side, since the photo of the follicle above clearly shows it apparently split in at least two places. Remember though, that this distinction is made when the fruit first opens, and in the photo above, the follicle had probably been present on the plant for quite a while. I'll try to get a photo that better shows this at some point (and not just because I feel bad for maybe stealing Tom's), but for now you'll have to take my word for it... well, I'll back it up with a story.

Back when I first started working at the Arnold Arboretum after finishing my undergrad, I had collected a few of these follicles (well, back then I knew them as "seed pods") off milkweeds as they were ripening, with hopes to do something with them later I guess (it was a flawed plan). I put these follicles in my locker where I apparently planned to leave them indefinitley (again, flawed plan). About two weeks passed, and I suddenly noticed one of the follicles had looked like it burst. It had just sort of popped, like an overstuffed suitcase that wasn't properly latched shut. Now is when the flaws in my plan should have become evident. The follicles were beginning to burst open to disperse their seeds, and one can easily tell by looking at the seed that the dispersal mechanism is "wind". All they needed was a source... like for example every time I opened or shut my locker door.

It took a good two to three months for the dispersal situation to die down enough for me to feel confident I could carry those follicles to the trash without making a bigger mess in the process.
Moral of the story: milkweed fruits split down one side. Keep them in a bag.

From Wikipedia's entry on the silique

Moving on, there are also two dehiscent fruits resulting from multiple carpels: the capsule, and the silique. Now these are considered simple fruits as well, since even though more than one carpal is involved, the carpels have not fused together tightly enough to produce a true aggregate fruit such as a pineapple or strawberry.

A silique is characteristic of the mustard family, a long fruit resulting from two carpels. The individual seeds are held in that central portion until both sides of the fruit split off, allowing their release.







Last but most common, is the capsule. It is also the result of multiple carpels, but in this case those that were  fused together in the a flower as a compound ovary.

The Poppy, displaying a compound ovary. We can make out
theanthers to the outside, but the female part of the flower
is a far cry from the distinct stigma/style of the Amaryllis.
From Wikipedia entry on  the Poppy

And from the same entry, the capsule ready to burst.

The capsule will sometimes split in half to release seeds, though sometimes it actually bursts at the top. Since capsules are a bit more common, there are a few different dispersal mechanisms, so the distinction here isn't quite as important as it was when differentiating the follicle from the legume. What's important to remember is that it forms from more than one carpel, since the flower proceeding it possessed a compound ovary.

So that's it for deshicent fruits. In summary: If it's from one carpal and splits down one side, it's a follicle, if both sides, it's a legume. If it's from a compound ovary, it's a capsule, and if it's a long fruit of a mustard resulting from two carpels, it's a silique.

Don't worry too much though if you're having a little trouble with this... My guess is that you're feeling you'd have trouble looking at a fruit and guessing how many carpels the flower that proceeded it had. I wish I had a few good cross-section photos of capsules vs. follicles to show which might make it easier, but for now I'll say the capsule will usually look a little more "full" on the inside than the more empty milkweed pod we started the entry with. Regardless, my main hope here is to have us gain an appreciation for these different types of fruits. We can work out the details later.

Next time I'll cover the indehiscent fruits, and will have a photo that is indisputably mine.