Anatomy: Acrostichum

Acrostichum

Fern Stipe Section or Petiole
Acrostichum
Green River Formation
Eocene
Wyoming, USA
2.5cm x 2.5cm

Many of the preserved Acrostichum petiole sections exhibit a conspicuous v-shaped adaxial groove. In transverse section the vascular bundles in some specimens can be seen to form a complex omega or horseshoe-shaped pattern (Arnold & Daugherty, 1963). Image of vascular bundle at 250x taken with a Dino-Lite AD7013 MT 5.0 MP.

When looking at a transverse section there is an interesting difference between the vascular bundles that line the sloping sides of the adaxial groove with those lining the rest of the periphery. Vascular bundles along the periphery of the adaxial groove have their protoxylem oriented towards the outside in contrast to the other peripheral vascular bundles that have their protoxylem oriented towards the inside (Arnold & Daugherty, 1963, p. 212).

Images of vascular bundles at 200x taken with a Dino-Lite AD7013 MT 5.0 MP and resized in Adobe Photoshop CS6. The first image shows vascular bundles along the periphery with protoxylem oriented towards the inside of the petiole. The second image shows vascular bundles along the adaxial groove with their protoxylem oriented towards the outside of the petiole.

Bibliography

Arnold C. A. & Daugherty L.H. (1963). The Fern Genus Acrostichum in the Eocene Clarno Formation of Oregon. Contributions from the Museum of Paleontology, The University of Michigan vol. 28, no 13, pp. 205-227.