Photo by Linda Lee This fern is quite common in the Southeast, stretching north into the Ohio River Valley and New England and west to eastern Texas. It grows in rather unspecialized places including fields and meadows as a variety of shady or open forests usually on the dry side.

Ferns are an interesting group of plants from an ancient lineage, all of them vascularized, with plenty of water- conducting internal plumbing. However, they don't produce any flowers, fruits, or seeds. They produce spores.

Spores are generally released from the plant out of specialized structures, sporangia, and after floating around in the air for a while, they settle down on the ground and sprout.

The resulting plant is very tiny and known as a gametophyte. The gametophyte is an ugly little thing that never attains a fern- like appearance and often stays completely below ground. The gametophyte is extremely important in the grand view of things because that's where the gametes, egg and sperm cells, are produced.

Following fertilization, a completely new plant body arises from the gametophyte. This new plant is what everybody recognizes as a fern complete with beautiful green leaves above the ground. The new plant is also where the spores come from, and the cycle begins again.

There is an alternation of gamete- producing and spore- producing plants within the same species. This cycle is referred to as alternation of generations and occurs in all the plants, not just ferns.

There are a few more curious and somewhat complicated details involved in plants' alternation of generations. This aspect of plant reproduction is as fascinating as it is biologically important. The sporophyte of our Mystery Plant produces a single, dark green frond, which does not produce any sporangia. It's sterile.

A second frond is produced and attaches just below the soil line, which will bear several grap- -like clusters of yellowish sporangia on its branches. This is the fertile frond. A new plant, sporophyte, will emerge from the ground in the summer, and the fertile frond sheds its spores by autumn. Then it dries up.

The sterile frond is evergreen and will last all winter. This species has a number of similar relatives, but they all have their sterile and fertile fronds fused together well above the ground.

Answer to this week's mystery plant

[Answer: "Southern grape-fern," Sceptridium biternatum]

Dr. John Nelson is the curator of the USC Herbarium. To learn more about the Herbarium, call 777-8196. The

department also offers free plant identification.

www.herbarium.org