Leathery Grapefern

Leathery Grapefern frond that has survived the winter intact on May 2, 2013.
Leathery Grapefern frond that has survived the winter intact on May 2, 2013.

Now that most of the snow has melted I am out looking for grapeferns. One that is common in this part of Minnesota is the leathery grapefern (Botrychium multifidum). The grapeferns are related to the moonworts such as the daisy-leaf moonwort (B. matricariifolium). Both are in the family Ophioglossaceae which includes another strange fern genus, the adder’s tongue ferns (Ophioglossum).

Leathery grapefern is in the subgenus Sceptridium (or genus according to some classifications) which includes several other species such as rugulose grapfern (B. rugulosum), dissected-leaf grapefern (B. dissectum), blunt-leaf grapefern (B. oneidense). The grapeferns, like the moonworts, have short subterranean stems with a few thick roots, fronds that are several times larger than the stem, and separate fertile and sterile fronds. They differ primarily in their broadly triangular fronds which are semi-evergreen and not ephemeral. The frond or tropophore of grapeferns will persist under the snow into the spring. This will wither once warm weather arrives and a new frond will slowly emerge to replace it. The new frond may take almost eight weeks to completely open. There is one frond, or rarely two fronds, produced per year. A sporophore is not always produced each year.

The tropophore of leathery grapefern is triangular, dark green, horizontally oriented, 4 to 28 cm long and 3.5 to 20 cm wide on a stipe to 6 cm. The pinnae are regularly divided to the tip, slightly overlapping to slightly spaced. The 4-8 mm wide pinnules are rounded to bluntly pointed; the margins are usually smooth or sometimes crenate to finely denticulate. Venation is pinnate. The sporophore of leathery grapefern is as large as the trophophore, 2-3-pinnate, and upright.

Leathery grapefern is widespread over North America and colonies of leathery grapefern can be composed of dozens or even hundreds of individuals. It occurs in variety of open, mesic grassy habitats, disturbed soils such as iron mine waste and dredge spoils if soil moisture is adequate, and in forests under light shade.

Leathery grapefern, and probably other Sceptridium as well, is a long-lived plant with estimates of at least one century. Age is estimated by the number of leaf scars on the stem. I have dug up two medium-sized plants and counted 25 leaf scars on the stems indicating that these plants were at least that many years old. I find it amazing that such small plants, herbaceous ones at that which do not produce rhizomes or offsets (clones), can be so long-lived.

References

Stevenson, D.W. 1975. Taxonomic and morphological observations on Botrychium multifidum (Ophioglossaceae). Madrono 23:198-204.

Wagner, Jr., W. H. and F. S. Wagner. 1993. OPHIOGLOSSACEAE. C. Arardh in Flora of North America Editorial Committee. Flora of North America. Vol. 2. Pteridophytes and Gymnosperms. Oxford University Press. New York. xvi + 475 pages.

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