Instead, the leaves arise directly from an underground stem rhizome or a very short vertical stem at or near the soil surface. Therefore, fern stems are often very inconspicuous and the portions of ferns most often noticed are the leaves. Each fern leaf is called a frond , and each fern plant may have from one to many fronds.
If an individual fern plant has more than one frond, they are often arranged in a conspicuously clumped arrangement, or less commonly they may be spread out along an underground stem. Fronds in some Wisconsin fern species may be as small as one inch long, or as large as 3 or more feet long in other species. The fronds of many species are herbaceous , dying back at the end of each growing season. New leaves are produced in the next growing season from the stem that overwinters at or below the soil surface.
A few ferns have fronds which remain green over winter. Ask Auckland. Main Menu Quick Links Please select root levels for the menu. NZ Plants. Sporangium Ferns are dispersed by air-borne spores which have a thick protective wall that surrounds a living cell.
Detached sporangia. Several sporangia. Ultraviolet microscope More on Davallia. In other ferns the sporangia are uncovered but are in groups. Sporangia covered by leaf margin. Add to collection. Transcript Frond dissection Fronds can be simple and undivided like the leather leaf fern, or pinnate once divided like the thread fern. Appears in. What is a fern? Add to favourites. Go to full glossary Add 0 items to collection.
Download 0 items. Twitter Pinterest Facebook Instagram. Email Us. See our newsletters here. Ferns with two kinds of leaves are referred to as dimorphic. Examples of dimorphic ferns are deer fern Blechnum spicant and cinnamon fern Osmunda cinnamomea. Deer fern Blechnum spicant. Cinnamon fern Osmunda cinnamomea. Photo by Linda Swartz. Other ferns, such as the moonworts have sterile pinnae and fertile pinnae on the same leaf. This can be seen in the moonwort fern Botrychium lunaria.
Sori singular: sorus are groups of sporangia singular: sporangium , which contain spores. Sori are usually found on the underside of the blade. Young sori are commonly covered by flaps of protective tissue called indusia singular: indusium. See the following graphic.
Sori can vary considerably in shape, arrangement, location and covering depending on the kind of fern. These differences can be useful for identifying ferns. However, depending on the time of year, sori and indusia may not be useful characters because they may be too immature or too mature to be diagnostically useful.
Sori without indusia. The sori of polypody ferns do not have indusia. Here we see the sporangia with no indusium. Sori with umbrella-shaped indusia. The indusium is round, shaped like a tiny umbrella and attached to the leaf from the middle.
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