It is in fact typically a closed system.
When we think of decoding the genome, we typically think in terms of the human genome.
The climate of Nebraska is typically inland or continental; i.e.
Typically Marattiaceous sori, consisting of exannulate sporangia united to form synangia, are frequent, and are almost always found on fronds with the character of Pecopteris, large, repeatedly pinnate leaves, resembling those of Cyatheaceae or some species of Nephrodium.
The longest-known genus and the one containing the largest species is Anchitherium, typically from the Middle Miocene of Europe, but also represented by one species from the Upper Miocene of North America.