5 - How Old are Ferns? (w/ Morgan Engler!)
5. How Old are Ferns?
Ferns are boring and they look like old houseplants! Well, slow your roll there. Some of these plant’s relatives were around before the mega-continent Pangea broke apart. Ferns apply to today’s research. Ferns give you an excuse to use words like fiddlehead, pteridology, and give each of us the chance to become a frond friend. Let’s learn to be scientifically conversational.
General Learning Concepts
1) What is a fern?
a. What is a plant? Any member of the kingdom Plantae, comprising multicellular organisms that typically produce their own food from inorganic matter by the process of photosynthesis and that have more or less rigid cell walls containing cellulose. They make their own “food” by being photosynthetic and store their food as starch. Plants are unable to move on their own because of their rigid cell walls made from cellulose. Vascular plants like ferns also have a completely different lifecycle called ‘alternation of generations’.
i. Alternation of Generations: The plant, which we recognize as a fern, is a sporophyte. The gametophyte is a small, heart shaped plant that contains both male and female sex organs. The gametophyte is fertilized into a zygote from a sperm and an egg, and the zygote grows using mitosis. The spores are formed from the plant using meosis.
b. What is a fern? Ferns are plants that do not have flowers (Class: Polypodiopsida). Ferns generally reproduce by producing spores. Similar to flowering plants, ferns have roots, stems and leaves. However, unlike flowering plants, ferns do not have flowers or seeds; instead, they usually reproduce sexually by tiny spores (or sometimes can reproduce vegetatively, as exemplified by the walking fern).
i. Structure: Ferns have leaves that are called fronds, made up of blades (“leaves”) and petioles (“Leaf stalks or “branches”). Unrolling fronds are called fiddleheads. Ferns have thin, wiry roots that grow along the stem.
c. How diverse are ferns? Today, ferns are the second-most diverse group of vascular plants on Earth, outnumbered only by flowering plants. With around 10,500 – 12,500 living species, ferns outnumber the remaining non-flowering vascular plants (the lycophytes and gymnosperms) by a factor of 4 to 1. Beyond this, horsetails are now defined as ferns.
d. Ferns are their relationships: Produce compounds to cause insect resistance including ferulic acid, hydrolysable tannins, terpenes, and alkaloids. Some animals eat spores of ferns which helps the distribution of the grown fern.
i. Mycorrhizas: Mycorrhizas are symbiotic relationships between fungi and plant roots (the term means literally 'fungus root'). To a large degree, mycorrhizas seem to be symbiotic (mutualistic) relationships, in which the fungus obtains at least some of its sugars from the plant, while the plant benefits from the efficient uptake of mineral nutrients (or water) by the fungal hyphae.
e. What is the distribution of ferns? Worldwide distribution; none in the Antarctic continent, some to many islands (Aruba, Phoenix, etc). Introduced and adventive species are also not counted.
2) When did ferns evolve?
a. Timeframe: Ferns are a very ancient family of plants. They predate the beginning of the Mesozoic era, 360 million years ago (argued to be even older, possibly 430 mya). By as early as the Triassic period (251 to 200 million years ago), evidence of ferns related to several modern families appeared. Still, most of the diversity of ferns that we see today came from around 70 million years ago.
i. Comparison to other old organisms: Sharks: 450 million years ago, oldest known shark scales found in Siberian deposits. Common relative between birds and crocodilians: 230 million years ago, Archosauria (ruling lizards). Late Triassic. Pangea: fully assembled by the Early Permian Epoch (some 299 million to 273 million years ago). The supercontinent began to break apart about 200 million years ago, during the Early Jurassic Epoch (201 million to 174 million years ago). Mammals: Some ancient mammals first started to develop around 230 million years ago (Eozostrodon: the shrewlike creature laid eggs but fed its young mother's milk). Dinosaurs: Non-bird dinosaurs lived between about 245 and 66 million years ago, in a time known as the Mesozoic Era.
b. Why would ferns go extinct? Competition for land and resources. Angiosperms (flowering plants that produce fruits and seeds) exploded into existence and challenged the fern population. Surviving ferns are likely still around because they can thrive under low light conditions by a photoreceptor called neochrome that can sense red and blue light within a single gene instead of two separate genes. This gene likely came from another primitive plant called a hornwart, passed by either a virus or a plant growing within the common boundary of the other.
a. Insect resistance: Azolla filiculoides, which is a fern species that forms mats on water, contains a gene that gave the fern resistance to insects. It is difficult to sequence fern genomes because they’re gigantic – averaging 12 gigabases (4x the human genome size). Azolla is only 0.75 Gb large.
b. Carbon sequesteration: A tiny, ancient fern called Azolla, excavated from the artic, was capable of fixing nitrogen and trapping CO2 at large rates (60 tons a year of CO2 per hectare, emissions of almost two hours of flight by a Boeing 747).
4) Fun Tidbits
a. What do The Lost World: Jurassic Park and Star Wars VI have in common? Both were filmed in the Redwoods State park in Northern California. Shots of The Lost World were specifically filmed in Fern Canyon in the Prairie Creek Redwoods State Park in Humboldt County: high walls covered in a variety of ferns.
b. How can I become a frond friend or a pteridologist? Pteriodology is the study of ferns and related plants. Frond Friends is a consortium of organizations of those who enjoy, study, or learn about ferns. For PA, there is a book called the Ferns and Fern Allies of Pennsylvania (35 dollars).
5) Solicited Naïve Questions
a. Why should I care about ferns? They provide microhabitats including shelter and shade to small animals. They act as a source of food for some animals. They’re culturally important. Capable of filtering toxins like heavy metals (makes sense, cattails). Often endemic species that co-evolve with other species.
b. What is the biggest a fern can get? Cyathea brownii or the Norfolk Island Tree Fern is the largest of the tree ferns. Growing fronds up to 6 meters (~20 feet) and 20 meters tall. [Some reference here is a little weak – “ferns are so simple they don’t know how to get sick”]
c. What is the rarest fern? Ascension’s endemic parsley fern, thought to be extinct as of 2003 and rediscovered in 2010. Four discovered plants (two, after two died quickly) were nursed until fronds produced spores by two scientists (Stedson Stroud and Olivia Renshaw) and a fertile frond was taken to a lab, grown to health, and cryogenically frozen.