Plant produces beautiful green leaves

  • Thursday, June 27, 2013

Photo by Linda Lee/USC Herbarium A second frond attached just below the soil line will produce several grape-like clusters of yellowish sporangia on its branches.

 It’s a fern, of course. This one 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 well as a variety of shady or open forests, usually on the dry side. It can handle a good bit of shade, so you can find it in the deep woods during a long hike, far from the parking lot.
Now ferns are an interesting group of plants from a very ancient lineage, all of them vascularized, with plenty of water-conducting internal “plumbing.” Ferns have vascular tissue in common with the gymnosperms (cycads, pines, cedars, cypress, etc.) as well as the flowering plants (orchids, roses, sunflowers, sand-spurs, etc.). But, ferns don’t produce any flowers, or for that matter, fruits or seeds. Instead, they produce tiny spores which act as their dispersal units. In a fern, spores are generally released from the plant out of specialized structures called “sporangia”, and after floating around in the air for a while, the spores commonly settle down on the ground somewhere and sprout. We are talking TINY here…with a resultant little plant that botanists call a gametophyte. The gametophyte is a rather drab little thing that never attains a fern-like appearance, and often stays completely below ground. The gametophyte is extremely important however, in the grand view of all things fernish, since 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,” frequently developing a rhizome down below, and with beautiful green leaves above the ground. The new plant is also where the spores come from, and the cycle can begin again. Thus, 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 it occurs in all the plants around us, not just ferns. As you might expect, 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, and yet for some reason, some of my students tend to get a bit drowsy and unresponsive during this particular lecture.)
The sporophyte of our Mystery Plant eventually produces a short rhizome, and each year it will send up a single, dark green frond, which does not produce any sporangia—it’s “sterile.” A second frond is produced, however, and attached just below the soil line, which will bear several grape-like clusters of yellowish sporangia on its branches. This is the “fertile” frond, which will shed its spores by autumn. Then it dries up. The sterile frond, though, is evergreen, and will last all winter. This species has a number of similar-looking relatives, but they all have their sterile and fertile fronds fused together well above the ground.
 
Answer: “Southern grape-fern," Sceptridium biternatum
 
John Nelson is the curator of the A. C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia SC 29208. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196, or email nelson@sc.edu.
 

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