Polypodiales

Fig. 1. Evergreen Wood Fern Dryopteris intermedia [3].

This order of ferns can be found anywhere from temperate to tropical climates. Including the fern pictured in Figure 1, which is commonly found in the North-Eastern U.S. and Canada [3].

Description

The Polypodiales order is extremely old and one of the most diverse plant orders extant today. Gene sequencing has determined Polypodiales to have diverged from other fern orders during the Mesozoic Era, in the Cretaceous Period [3]. Polypodiales represent almost 80% of extant fern species in the world [2]. This order displays distinct characteristics for identification, which include sporangia that are connected to a vertical annulus interrupted by the stalk and stomium. Additionally, the sporangial stalks typically are 1-3 cells wide. [7] While growing, their gametophytes are green and heart shaped as seen in Figure 3 [7]. Additionally, polypodiales have a special photoreceptor called a neochrome, which combines red and blue sensing organelles for more efficient photosynthesis [6]. This specialized photoreceptor aids the fern in low-light conditions, allowing effective photosynthesis in areas such as the forest floor.

Fig. 2. Taxonomic tree for polypodiales lineage developed by PPG I [5].

Scientific Classification
Kingdom	Plantae
Phylum	Tracheophytes
Class	Polypodiopsida
Order	Polypodiales

Phylogeny and Classification

The sub-orders within polypodiale have had numerous rearrangements since their initial taxonomic placements. Research within the 21st century has redefined the sub-order and subfamily structure of polypodiales. An expansive collaboration called the Pteridophyte Phylogeny Group (PPG I) was done in 2016 to complete this task, creating the three major sub-orders comprised of eupolypods I, eupolypods II, and cathetogyrates [8][5]. The cathetogyrates is a collection of sub-orders not in eupolypods consisting of Dennstaetiinae, Pteridineae, Lindsaeineae, and Saccolomatineae, seen in Figure 2 [5]. Further classification methodology has been researched based on the re-evaluation by PPG I, including analysis of Leaf Architectural Characters. [8] The research provided empirical evidence and methodology to observe structural characteristics between the suborders and families; further verifying the re-classification done by PPG I [8].

Life Cycle

As seen in Fig 3, a spore grows into a heart-shaped gametophyte containing both sex organs. Once fertilized this gametophyte slowly grows creating its own rhizosphere and begins sprouting the fronds or sporophytes. Over time these sporophytes grow into the widely recognized fern fronds. Once mature the fronds will grow spore nodules known as the sporangium underneath the leaves. Eventually, these sporangia will burst, releasing the spores into the air/water allowing them to grow into gametophytes and restarting the process once more.

Fig. 3. Life cycle for a fern, note the heart shaped gametophyte [1].

Sources

[1] Bioweb. (n.d.). Retrieved April 21, 2022, from https://www.sas.upenn.edu/~joyellen/bioweb.html

[2] Contributors, W. 2022, April 21. Polypodiales. Wikipedia, The Free Ecyclopedia. https://en.wikipedia.org/wiki/Polypodiales

[3] Du, X.-Y., Lu, J.-M., Zhang, L.-B., Wen, J., Kuo, L.-Y., Mynssen, C. M., Schneider, H., & Li, D.-Z. (2021). Simultaneous diversification of Polypodiales and angiosperms in the Mesozoic. Cladistics, 37(5), 518–539. https://doi.org/10.1111/cla.12457

[4] Evergreen Wood Fern. (n.d.). Retrieved April 21, 2022, from https://www.dept.psu.edu/nkbiology/naturetrail/speciespages/evergreen_wood_fern.html

[5] I, P. (2016). A community-derived classification for extant lycophytes and ferns. Journal of Systematics and Evolution, 54(6), 563–603. https://doi.org/10.1111/jse.12229

[6] Li, F.-W., Villarreal, J. C., Kelly, S., Rothfels, C. J., Melkonian, M., Frangedakis, E., Ruhsam, M., Sigel, E. M., Der, J. P., Pittermann, J., Burge, D. O., Pokorny, L., Larsson, A., Chen, T., Weststrand, S., Thomas, P., Carpenter, E., Zhang, Y., Tian, Z., … Pryer, K. M. (2014). Horizontal transfer of an adaptive chimeric photoreceptor from bryophytes to ferns. Proceedings of the National Academy of Sciences of the United States of America, 111(18), 6672–6677. https://doi.org/10.1073/pnas.1319929111

[7] Smith, A. R., Pryer, K. M., Schuettpelz, E., Korall, P., Schneider, H., & Wolf, P. G. (2006). A classification for extant ferns. TAXON, 55(3), 705–731. https://doi.org/10.2307/25065646

[8] Tan, J. M. P., & Buot, I. E. (2019). Cluster and Ordination Analyses of Leaf Architectural Characters in Classifying Polypodiales sensu PPG. 17.