Biology
Easy to grow...
Ferns of our times are the descendants of plants that existed almost 400 million years ago. There are more than 10000 different species today and their habitat reaches from dampy swamps to drylands and deserts. For many centuries it was unclear how ferns propagate; indeed, they have a very interesting sex life! Since ferns developed - when there were no insects on earth to pollinate them (like they do on flowering plants) - they propagate via spores, very small and dust-like cells that are blown over and fill the air ever since.
The omnipresence of these spores make ferns very successful plants. Due to their large genome (the average number of chromosomes in homosporous ferns is 57 [2]) one can see that ferns carry a rich biological heritage.
Most fern species can be found in the tropics where they grow in a warm and humid climate. These conditions are somewhat imitable at home as long as you heat your flat and provide some humidity. This makes your bathroom and your kitchen a possible fern oasis. However, ferns can get quite touchy when treated the wrong way. There are a lot of possible mistakes and misunderstandings that can lead to illness and plant death. So a plant's attribute "easy to grow" doesn't mean that you just put it in a pot and add some water (though this wouldn't be a bad start!). We had our own failures and collected some dos and don'ts that hopefully will help you.
Pteridophytic basics
Taxonomy means the theory and practice of classification of organisms while Systematics means the science of polymorphism of organisms and comparing among themselves. The hierarchic classification goes as follows: A family consists of one or more genera. A genus consists of one or more species (if it's only one, it is calles a monotypical genus). A genus may be divided in multiple sections. [2],[3]
Pteridophytes are vascular plants with independent gametophytes and motile sperms, usually classified into 4 divisions/classes with 40 families (there are 3 other classes that are completely extinct). The 9000 species are made of approx. 365 genera, and are growing in many habitats. Most of them prefer a moist and shady environment though some of them are able to survive in extreme climates. Many species (approx. 2500) are epiphytes and live on trees (without being parasitic).
Ancestors of Pteridophytes definitely were the first vegetable organisms that left the water and cultivated the landmass. Many developments that can still be seen on modern plants of today were already done several hundred million years ago. This includes:
- The build up of the vergetational body consists of differenciated tissues and organs. During the generation cycle there is more emphasis on the diploid sporophyte than on the haploid gametophyte.
- Emergence of stabilizing vascular tissue and the cuticula, a protective layer.
- Anchorage of the plant in the soil. Propagation through spores.
In former times, classification of Pteridophyta was characterized by the nature of their sporangia (you may find this classic organization in present texts, though):
- Eusporangiate: several initial cells develop a large sporangium with many spores
- Leptosporangiate: a single initial cell develops small sporangia with a small amount of spores
But there is small evidence of a relationship between Ophioglossatae and Marattiales.
Usually, Pteridophytes are subdivided into following classes (classes marked with an * are extinct):
- Rhyniatae ( = Rhyniopsida) *
- Zosterophyllatae (= Zosterophyllopsida)*
- Trimerophytatae (= Trimerophytopsida)*
- Lycopodiatae (= Lycopsida, Lycopodiophyta; club and spike mosses, quillworts)
- Equisetatae (= Sphenopsida, Equisetophyta; horse-tails)
- Psilotatae (= Psilotopsida, Psilotophyta (whisk ferns))
- Filicatae (= Pteropsida, Polypodiophyta; "true" ferns, all others are "allies")
K. R. Sporne's classification lists four subclasses of Filicatae that are subdivided in further orders [4]:
- Primofilicidae (extinct, anchestors of modern ferns) *
- Cladoxylales *
- Coenopteridales *
- Eusporangiatidae
This subclass includes rather primitive ferns. Sporangia are developed in a different way than in the Leptosporangidae group.- Marattiales
- Ophioglossales
- Osmundidae (Osmundales, this species takes an intermediate position between Eusporangiatidae and Leptosporangidae. They may be considered "living fossiles".)
- Leptosporangidae
- Filicales (Filicales make the biggest group of all Pteridophytes (9000 species approx. in ca. 300 genera)).
- Marsileales
- Salviniales
But the taxonomy of ferns is still argumentative. Kramer et al. [2] dispense with positioning orders but lists subclasses of true ferns with supposed relationships (further subdivisions give families and genera):
- Ophioglossatae
The fertile leaf is diveded in a sterile and a fertile section (sporophor). Rhizome with collateral vascular bundles. Botrychium with secondary lateral growth.- Ophioglossaceae (Botrychium, Helminthostachys, Ophioglossum)
- Filicatae
No secondary lateral growth at all, rhizome with proto-, soleno-, or dictyostele, supporting tissue. Sporangia to be found on leaves. Gametophyte autotroph.- Marattiales (Marattiaceae, very old family, reaching back to carboniferous.)
- "Filices Leptosporangiatae"
- Osmundacae (primitive family of leptosporangiate ferns, big ferns)
- Plagiogyriaceae
- Matoniaceae (Old, primitive family reaching back to palaeotropics.)
- Dipteridaceae (Relict of Mesozoic ferns.)
- Cheiropleuriaceae (Again an old family.)
- Loxomataceae
- Gleicheniaceae (Widely spread, old family. Frond branching remarkable.)
- Schizaeaceae (Old family of uncertain relationship.)
- Hymenophyllaceae
- Dicksoniaceae (One of the tree fern families.)
- Lophosoriaceae
- Metaxyaceae
- Cyatheaceae (The other tree fern family.)
- Hymenophyllopsidaceae
- Dennstaedtiaceae
- Monachosoraceae
- Pteridaceae
- Vittariaceae
- Thelypteridaceae
- Polypodiaceae
- Grammitidiaceae
- Dryopteridaceae
- Oleandraceae
- Nephrolepidaceae (This group contains the famous Boston fern.)
- Davalliaceae
- Lomariopsidaceae
- Blechnaceae
- Aspleniaceae
- Marsileaceae
- Salviniales (Former group of water ferns (Salviniaceae, Azollaceae)).
- Fern allies:
- Equisetatae
- Lycopodiatae (Lycopodiaceae, Selaginellaceae, Isoetaceae)
- Psilotatae (Psilotaceae)