Family Ericaceae and related families (Unit 016)

1. Mycorrhizal Fungi

Mycorrhizal fungi are fungi associated with plant root systems in a symbiotic

or beneficial relationship. The fungi mycelia can obtain nutrients that are useful to the

plants. The fungi also are tied to the roots of forest trees.

The family Monotropaceae is closely related to the Ericaceae, and has no chlorophyll.

It is dependent on the mycorrhizal fungi for all of its nutrients. Leaves are reduced and

scale like. These plants are often fleshy, and colored white (see Monotropa uniflora for

pictures), pink, red, purple, yellow, or brown, but not green since they lack chlorophyll.

The family Ericaceae has many genera and species that grow best with some mycorrhizal fungi.

This is also true with the family Pinaceae (Unit 11), where mycorrhizal fungi

inwoculation is important for good seedling growth. Some authors state that most of

the gymnosperms have mycorrhizal fungi associations.

Both the Cruciferae or Brassicaceae (Mustard Family), and the Chenopodiaceae

(Goosefoot Family) apparently have no mycorrhizal root fungi.

One reference estimates that 83 % of the Monocots and 79 % of the Dicots have

mycorrhizal root fungi.

Studies have also shown that some roots on a plant may be heavily colonized

by the fungi, while other nearby roots may be free of the fungi.

2. Parasitism and the Ericaceae

The Ericaceae, Pyrolaceae, and Monotropaceae represent progressive stages in

dependence on a mycorrhizal fungus.

The Monotropaceae usually have no chlorophyll, and are totally parisitic. They have

reduced scale-like leaves. They are completely dependent on their associated

fungus for food as well as water and minerals.

The Pyrolaceae usually have green leaves (some species are leafless),

but are somewhat dependent on mycorrhizal fungi. They are mostly evergreen,

perennial herbs from creeping rhizomes. The leaves are mostly basal. The

Pyrolaceae are most abundant and diversified in temperate and boreal regions.

The Pyrolaceae and Monotropaceae have the reduced embryo that often

accompanies parisitism or extreme mycotrophy, as found in other plants.

Many of the Ericaceae are more or less strongly mycotrophic (the symbiotic

relationship between a fungus and a living plant.)

3. Broadleaved plants

Since many of the Ericaceae are evergreen, winter protection is important since leaves

can lose water and turn brown in the Michigan winters.

4. Acid soil important

Most Ericaceae grow best in acidic soils. However, they may survive for a few

years in more neutral soils, before they start to decline.