Gardening Newsletter - February 2003, Issue 6
Having just returned from a vacation in the Caribbean, I thought I'd focus on some plants that people typically think of as tropical - ferns. But as you're about to read, there are ferns that do well in most corners of the earth.
My typical winter project - adding more plants to the Shade Plants and Shade Trees Encyclopedia - is nearing closure. I'll be adding around 40 new plants, and updating many of the others.
There are approximately 10,000 species of ferns. They range in size from tiny moss-like coverings to the massive tree ferns with stout trunks more than 80 feet tall. As ferns grow wild in all parts of the world, there are hardy and tropical varieties.
Ferns are fascinating plants, predating the dinosaurs. The ferns that grow today are very similar to those in fossil remains.
Like most modern plants, ferns are vascular. That is they have internal vein structures that carry the flow of water and nutrients. However, they reproduce in a very different manner than other contemporary plants.
Flowering plants reproduce when the pollen from a male flower fertilizes a female flower. Of course, many flowers have both male and female parts. Both the male pollen cell and the female cell contain half of the genetic material needed to produce a new plant. Once the genetic material of these two cells is fused together the fertilized cell grows into a seed capable of producing a new plant. The reproductive cycle of ferns is much more complicated than this.
To help us understand the reproductive cycle of ferns we first need to understand a fern’s physiology. The leafy branch of a fern is called a frond. The individual leaflets that make-up a frond are called pinnae. On the underside of many pinnae are small spots called sori. This is where a fern produces spores. Not every frond produces spores. Those that do are referred to as fertile fronds.
The sori release spores to the environment. Spores are roughly the size of grains of sand and come in shades of black, brown, red, yellow and, green. Unlike a seed with a complete set of chromosomes, each spore contains only half of the genetic material typically found in an adult fern.
Each spore is capable of growing into a tiny plant, less than a half-inch across, called a prothallus or gametophyte. The gametophyte is not a fern, but rather the intermediate stage between spore and adult fern. Like a spore, it contains only half of the genetic material of an adult fern.
The gametophyte has a set of male and a set of female reproductive organs on its underside. The male reproductive parts, called the antheridia, contain sperm cells, while the female reproductive parts, called the archegonia, contain eggs. The antheridia is separated from the archegonia by a slight distance. If there is a film of water on the underside of the gametophyte, the male sperm cells will swim towards the egg cells in the archegonia. This may be on the same gametophyte, or on neighboring gametophytes.
Once the sperm and egg cells fuse their genetic material, the new cell has the full genetic complement of an adult fern. The cell grows and divides within the gametophyte. Gradually it takes over the gametophyte and becomes an adult fern.
Ferns can reproduce in other ways too. Like many contemporary plants, ferns can also reproduce from spreading rhizomes. Brackenferns often spread this way. They can also sprout baby ferns on the tips of fronds. When the parent frond droops and touches the ground the baby roots. Of course the babies produced in both these manners are genetic clones to the parent plant.
Even more unusual, a fern can grow from a gametophye without fertilization. This is called apogamy.
To learn more about ferns visit the American Fern Society’s website: http://amerfernsoc.org
Some of My Favorite Ferns
The following are some of my favorite hardy ferns.
Polystichum acrostichoides (Christmas fern)
Christmas fern (Polystichum acrostichoides) is bushy and evergreen. The fronds are leathery and lance shaped. Grow it in part shade in moist well-drained soil. Divide it in spring.
This is perhaps my favorite fern. I love its fronds, which are a light brown, fuzzy and curvy. The undersides of the fronds have sori arranged in rows.
The botanical name refers to these rows of sori. It is derived from the word poly, meaning many and, stichos, meaning rows.
Christmas fern is hardy to zone 3.
This is a real beauty! Cinnamon fern has a clump forming habit. Its’ interior fertile fronds resemble large cinnamon sticks. Its’ fronds turn yellow or golden brown in autumn. Grow it in partial shade in moist, acid soil. It can take full sun if provided enough moisture. Divide cinnamon fern in spring or fall.
Cinnamon fern is hardy to zone 3.
Athyrium goeringianum (Japanese painted fern)
Athyrium goeringianum or Japanese painted fern differs from most ferns in that it is variegated. The fronds are silver edged with green and the veins and stems are deep red. This coloring intensifies when the plant is in partial shade opposed to full shade.
This is not an evergreen fern. When the cold winds come in the fall its fronds will dry-up and blow away. However, in the spring new fronds will spring-up.
The name Athrium comes from two words: “a” meaning not and “thyreos” meaning an oblong shield.
Japanese painted fern is hardy to zone 5.
Matteuccia struthiopteris (Ostrich fern)
This fern has an upright habit. The outer fronds are quite lacey. The interior fertile fronds bear spores on their lower surface. Grow ostrich fern in shade in moist, rich soil. Divide it in the spring or fall.
Large Decaying Leaves Promotes Disease
Leaf mulch is an excellent means to insulate plants from temperature extremes and retain soil moisture. However, the leaves should be shredded before they are used as mulch. Large, wet, decaying leaves may not only promote diseases such as crown rot, they may also harbor insects. Remove large leaves from new growth penetrating the ground.
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