Commonly Confused N.C. Ferns

Series I: 

Onoclea sensibilis vs. Woodwardia areolata

Many people have trouble distinguishing between Sensitive Fern, Onoclea sensibilis, and Netted Chain Fern, Woodwardia areolate, especially when the fertile fronds are not visible. At a quick glance they are very similar (Table 2) but, once you know what features to focus on they are easily identified!

Onoclea sensibilis or Sensitive Fern is a medium sized fern found commonly in all three regions of North Carolina. The common name ‘Sensitive Fern’ is derived from the fronds being easily damaged and dying when exposed to frost, even a light frost. The ferns are also ‘sensitive’ to drought and extreme exposure to direct sunlight ^{1, 2}. It grows in low wet areas such as wet ditches, marshes, swamps, and along stream margins. The ferns are dimorphic with separate and distinct fertile and sterile fronds. The sterile frond is one-pinnatifid with obvious wings along the rachis connecting the opposite pinnae. The lower pinnae may be one-pinnate and are sinuate to deeply lobed (Figures 1, 3). All pinnae have rounded tips (obtuse) and entire margins (Figure 3). The fertile frond is characterized by rows of rounded bead-like sori that quickly turn brown (Figure 5).

Woodwardia areolata or Netted Chain Fern is a medium sized fern found across the state but more commonly in the lower piedmont and coastal plain. The common name is derived from the unique elongated sori arranged in chains (Figure 6, 7).The ferns grow in moist habitats similar to Sensitive Fern. Plants are dimorphic and the sterile fronds are one-pinnatifid with obvious wings connecting the alternating pinnae, the lower pinnae may be one-pinnate. (Figure 2).  On some plants pinnae may be sinuate but they are never lobed as in Sensitive Fern. Pinnae are pointed at the tips (acute to acuminate) and are finely toothed (serrulate) on the margins, ² you may need a hand lens to see this latter feature (Figure 4). The fertile frond is one-pinnate with very narrow linear pinnae. The sori are elongated and arranged in chains along both sides of the costa (Figure 6, 7). 

Table 1: Historical and Current Taxonomic Treatment of Polypodiaceae in North Carolina

Common Name(s)	Radford & Bell 3 (1968)	Flora of North America 4 (1993)	Weakley 5 (2015)
Netted Chain Fern	Woodwardia areolata (L.) Moore	Woodwardia areolata (L.) Moore	Lorinseria areolata (l.) C. Presl.
Sensitive Fern	Onoclea sensibilis L.	Onoclea sensibilis L.	Onoclea sensibilis L. var. sensibilis

Table 2: Onoclea sensibilis vs. Woodwardia areolata

Onoclea sensibilis Shared Traits Woodwardia areolata Sensitive Fern Medium sized ferns Netted Chain Fern Pinnae mostly opposite Moist environments Pinnae mostly alternate Pinnae tips rounded Fronds triangular in shape Pinnae tips more pointed Pinnae margins entire Sterile fronds one- pinnatifid except lower pinnae may be one-pinnate Pinnae margins finely serrated Fertile fronds - sori bead-like Deciduous Fertile fronds - sori elongated in chain-like rows Dimorphic

I use the letter “O” in Onoclea to remind me that the pinnae are rounded at the tips and the margins are smooth (entire). Also the letter “O” stands for opposite pinnae.

Figure 1: Onoclea sensibilis sterile frond with oppositely arranged 
pinnae that have rounded tips and entire margins. 

I use the letter “W” in Woodwardia to remind me that the pinnae are pointed at the tips and serrated.

Figure 2: Woodwardia areolata sterile fronds showing
the alternate pinnae and their pointed tips.

 

Figure 3: Onoclea sensibilis pinna with entire margins and lobing.

 

Figure 4: Woodwardia areolata pinna showing
the pointed tip and finely serrated margins.

Figure 5: Onoclea sensibilis fertile frond traits, note the bead-like sori.

Figure 6: Woodwardia areolata plant with fertile and sterile fronds.

 

Figure 7: Woodwardia areolata fertile frond,
note the elongated sori arranged in chains.

Resources:

1. Common Name. Penn State University, 2002. Web. 13 June 2017. <http://www.psu.edu/dept/nkbiology/naturetrail/speciespages/sensitivefern.htm>.

2. "Onoclea sensibilis." Onoclea sensibilis - Plant Finder. Missouri Botanical Garden, n.d. Web. 13 June 2017. 

<http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=l300>.

3. Radford, Albert Ernest, Harry E. Ahles, and Clyde Ritchie Bell. Manual of the vascular flora of the Carolinas. Chapel Hill, NC: U of North Carolina Press, 1983. Print.

4. Morin, Nancy R. Flora of North America North of Mexico Volume 2: Pteridophytes and Gymnosperms. New York, NY: Oxford U Press, 1993. Print.

5. Weakley, Alan S. Flora of the Southern and Mid-Atlantic states. Chapel Hill, NC: U of North Carolina Herbarium, North Carolina Botanical Garden, U of North Carolina, Chapel Hill, 2015. Print.