GEOG/ES&P 330
California Ecosystems
Fruits and Seeds
The culmination of flowering plants' reproductive efforts, fruits and seeds can be helpful in the process of trying to identify a plant, if the plant has begun fruiting or set seed by the time you're out in the field.Technically, a fruit is the ripened ovary and associated bits containing seeds, while a seed is a ripened ovule, containing the embryo and enough stored food to sustain it through the process of germination and the early development of the seedling.
Types of Fruit
Fruits can be broadly classified as fleshy fruits and dry fruits. This has a lot to do with how the plant gets its seeds out and about where they can land someplace safe to germinate and, hopefully, away from the competition of the adult parents. Their strategies might entail recruiting "someone else" to grab their fruit and haul it away, or eat it and deposit the seeds it contains out the other end. This strategy requires investing possibly scarce energy into the production of some tasty inducement to these third parties, which is expensive per seed. Another strategy is to exploit mechanical transportation opportunities, as by making fruit easily moved by wind or water (or snagged in the coat of animals). This is cheap per seed but expensive per successful seedling in the sense that this is a more scattershot approach and it requires the production of prodigious amounts of seeds to make it work.Fleshy Fruit (all of these are "indehiscent," the seeds staying attached to the fruit until opened up by an animal or just the process of decay)The tasty, inviting fruit represents the hyperdevelopment of the ovary wall (pericarp, usually the mesocarp or middle level) and sometimes other nearby bits are brought in, such as the receptacle (the thickened end of the peduncle or flower stem, which supports the flower). It might help to see a labeled diagram of these parts:Dry Fruit (some seeds stay with the fruit; others are "dehiscent," meaning the fruit breaks open to release the seeds)Fleshy fruits can be analyzed further by the source of the seeds they carry. Sometimes there is one seed, which came from one flower that had a single pistil with a single locule in it: a simple fruit. Sometimes, several in a single flower can fuse to form a single fruit, a kind of compound fruit. Other times, there may be a cluster of such one-seeded fruits, each fruit coming from a separate floret in an inflorescence that then all crowd together to create what we think of as a single fruit (a kind of compound fruit). Here are various types of fleshy fruits:
- Flower (perfect bisexual flower)
- Pericarp divisions
- Drupe has a fleshy pericarp, or ovary covering, which surrounds a single seed encased in a stony endocarp, e.g., a peach, prune, cherry, olives, or coconut. A local example would be Prunus ilicifolia or holly-leaf cherry
- Aggregate has several drupe-like individual fruits coming out of th same receptacle. The receptacle isn't fleshy the way it is in an accessory, and, unlike the classic drupe, these don't occur singly but in groups descended from multiple pistils in the same flower. Blackberries, boysenberries, and raspberries are examples, and locally there's Rubus ursinus or California blackberry
- Multiple fruit can superficially resemble an aggregate, for example, a mulberry strongly resembles a blackberry. They differe from aggregates in that the individual drupes are not descended from several pistils in the same flower but from several separate florets within the same inflorescence, which then crowd together and merge, becoming a single unit. A local example is the Platanus racemosa or California sycamore.
- Berry is a fleshy fruit that contains more than one seed. The pulpy or fleshy material is formed from the compound ovary itself, which is superior or placed above the petals and sepals. A lot of the plants colloquially called berries aren't (such as blackberries and raspberries) and some of the true berries would seem startling to non-botanists (such as tomatoes, chili peppers, and bananas). Some familiar true berries are blueberries, grapes, gooseberries, currants, and cranberries. A local example is the Ribes speciosum or fuschia flowered gooseberry.
- Pepo is a fleshy fruit that, like a berry, forms from a compound ovary but, unlike a berry, forms a rind, like a watermelon. A local example is Marah macrocarpa or wild cucumber.
- Accessory is also a fleshy fruit, except the fleshy part is not the pericarp. Instead, it's the receptacle or the thickened part of a stem where the flower organs develop. In the case of an accessory, the receptacle develops into a fleshy mass attractive to potential distributors. The seeds are small and dry (achenes) studding the receptacle, as in strawberries. A local example is Fragaria vesca or California strawberry.
- Pome is a fleshy fruit most resembling an accessory fruit in that the fleshy part is developed from the flower receptacle. Unlike an accessory fruit, a pome contains its seeds within a core, rather than carrying them on the outside. The outer core corresponds to the endocarp of a drupe and is often leathery, sometimes stony. Apples are the classic example (apples are called "pommes" in French), as are pears. Locally, Heteromeles arbutifolia or toyon produces pomes (except don't even think of eating these: highly toxic!).
A dry fruit is often well suited to dispersal by the wind, though dispersal can also occur via water or by being stuck in an animal's coat). Some dry seeds are palatable to animals and many of these have become indehiscent, so they can hitch a ride via the animal somewhere else. Many others are dehiscent, some even snapping open and dispersing seeds almost explosively. Dry fruit can be analyzed further by the number of seeds: one or multiple.
- Single Seeded Dry Fruit
- Achene is a dry one-seeded fruit, which attaches to the pericarp or ovary covering or the swollen receptacle at a single point. An example is the strawberry, with achenes attached to the fleshy receptacle on the outside. Sunflowers also produce achenes, including Encelia californica or and another local example would be Baccharis pilularis or coyotebrush. These often feature a pappus or fluffy banner on a small stalk attached to the achene, usually derived from the calyx of an individual floret in the compound head of the Asteraceae (or composites).
- Samara is a dry fruit, basically an achene with wings that enable wind dispersal of the seeds. A local example would be Acer macrophyllum or big-leaf maple
- Caryopsis is a dry one-seeded fruit, but, unlike an achene, the seed is embedded in and connected at all points to the surrounding pericarp and can be hard to spot in there. A corn kernel is an example, and a native plant illustrating the concept is Orcuttia californica or California Orcutt grass found in coastal wetlands and vernal pools.
- Multiple Seeded Dry Fruit
- Multiple Seeds from a One-Celled Fruit
- Follicle is a dry one-celled fruit, which splits down one side to release seeds. A local example is Asclepias californica or California milkweed (critical butterfly habitat).
- Legume is a dry one-celled fruit with multiple seeds lining a pod, which splits down both sides to release them. A local example would be Lupinus bicolor or bicolor lupine
- Multiple Seeds Coming from Two or More Cells (locules in a compound ovary or multiple pistils/carpels in a single flower)
- Siliques and silicles are dry two-celled fruits, the two cells pulling apart at maturity, leaving the central septum or dividing wall between the cells, exposing the seeds attached to it. Siliques are long and thin, and silicles are squatter. Mustards illustrate the concept, and a native example is Erysimum capitatum or the western wallflower.
- Capsule is a dry fruit that breaks open to release seeds (dehiscent). It descends from more than one carpel/pistil. Some break open by pores, others by splitting along septa, still others by splitting each locule between septa, and some pop open like a lid. Eschscholzia californica or California poppies are local examples of capsule-bearing flowers.
