Apiaceae
Contents
Family size
Morphology
-inflorescence
- Vegetative    features

 

The Apiaceae is one of the large families of angiosperms, having around 300 genera and 2,500-3,000 species. It occurs throughout the world, but it is most common in temperate regions and rare in the tropics. It was first recognized as a distinctive group towards then end of the 16th century, making it one of the first families to be recognized as a distinct unit. It was also the first group of plants for which a systematic study has been published, this having been accomplished by Robert Morrison in 1672. This information is of minor importance, but it does suggest that the family is probably easy to recognize and well-represented in the European flora.

The most obvious distinctive feature of the family is the inflorescence, which is a simple or compound umbel. In a few genera, this is reduced to a single flower; in others, the rays and pedicels are lost so the inflorescence becomes a head or capitulum, but these variants do not occur in Utah. The family also has distinctive vegetative features. Almost all its members are herbaceous, have hollow stems, and alternate, compound, estipulate leaves that have a petiole with an expanded base that sheaths the stem, commonly referred to as a sheathing petiole.

The flowers of the Apiaceae are very uniform, most of the variation being in the leaves and fruits. Each flower is 5-merous but the calyx segments are sometimes reduced or even absent. The corolla varies from radially symmetric to strongly bilaterally symmetric, often within a single inflorescence. When the variation is within an inflorescence, the flowers towards the outside of the inflorescence are generally most bilaterally symmetric, whereas those towards the center of the inflorescence are radially symmetric.

Individual flowers of the Apiaceae are small; by themselves, they would not be readily apparent to pollinators. The inflorescence, however, is highly visible, and it is this that is the attractant. Having bilaterally symmetric flowers towards the outside of the inflorescence tends to make the inflorescence as a whole resemble a single flower. A similar trend is seen in the Asteraceae.

The androecium consists of 5 stamens, but there is often variation in the functionality of the stamens even within a single inflorescence, some of the flowers being functionally staminate and some functionally pistillate. Being functionally staminate means that a pistil may be present, but it has no ovules capable of being fertilized. Similarly, functionally pistillate flowers have stamens, but their anthers do not produce viable pollen. This tendency to bisexuality within an inflorescence promotes geitonogamy, pollination by a different flower of the same plant. This promotes some genetic diversity, but not as much as xenogamy, in which pollination is by a flower belonging to another plant. Another way of promoting geitonogamy that is found in many members of the Apiaceae is to have the stamens and pistil mature at different times. In the Apiaceae, the stamens usually mature before the pistils, a situation which is called protandry; if the pistil matures first, the term is protogyny.

The gynoecium of the Apiaceae consists of a single, bicarpellate pistil with an inferior ovary. When immature, the ovary consists of two fused carpers but, at maturity, the carpers separate from the bottom upwards. The fruit is described as a schizocarp, i.e., an ovary that splits, and each portion as a mericarp, or half-fruit. The mericarps are held to the plant for a short time by two carpophores, stalks that extend from the top of the receptacle to the top of each mericarp. The carpophores often remain attached to the plant after the mericarps fall.

The walls of the mericarps are often ridged or winged over the veins, sometimes very elaborately so. Because such ornamentation is important in identification, it is much easier to identify members of the Apiaceae if at least some mature fruits are present. Bear this in mind when collecting. The wall also contains oil ducts for oils that make so many of the Apiaceae important in cooking (for instance dill, caraway, coriander).

The top of the ovary often forms a stylopodium. A stylopodium resembles a plump cushion that has been pushed down in the center where the two style branches are attached. It secretes nectar and is, therefore, part of the insect-attraction repertoire of the plant. It may mislead you into thinking the ovary is superior, but a long-section will convince you otherwise.

Most members of the Apiaceae are promiscuous. This means that they can be pollinated by almost any critter that can walk over the surface of the inflorescence. They are generally self-compatible, so most pollination is geitonogamous. The pollinators are usually things like flies, mosquitoes, gnats (nice to find some use for these critters), and unspecialized bees.

Many members of the family will be found in the kitchen, e.g., Daucus carota (carrot), Pastinaca sativa (parsnip), Apium graveolens (celery), Carurn (caraway), Anethum (dill), Coriandrum (coriander), Cuminum (cumin), and Pimpinella (anise). A few species are used in medicine, but the most famous non-food member of the family is poison hemlock, Conium maculatum. It was this that was used to execute Socrates. All parts of the plant are poisonous. NEVER eat white-flowered members of the Apiaceae with purple markings on the stem. If you have ANY doubt, do not eat any white-flowered umbel. It does not take much to cause death. Around 1985, three campers in southern Idaho died because they mistook poison hemlock for Queen Anne's lace, which is the same species as the domesticated carrot.  Both are white-flowered members of the Apiaceae.

Like many of the families that were recognized early on, the Apiaceae has an alternative family name, Umbelliferae. I much prefer that name because it tells you one of the distinctive features of the family, but Shaw prefers Apiaceae, and he wrote the book we use. Welsh et al. use Umbelliferae in A Utah Flora. Both are legitimate; which one uses is a matter of personal preference UNLESS you follow Judd et al. - as we are doing. Judd et al. are NOT using Apiaceae in the traditional sense so one cannot use the traditional name for the family as they interpret it.

heracleum sphondylium.jpg (179566 bytes)
Heracleum sphondylium showing an umbellate inflorescence
LolHeracleum.jpg (92301 bytes)

Large sheathing leaves