One of the distinguishing features of these ferns is the shape of the cross-section of the midrib near the base of the frond. The accompanying drawing of these shapes is taken, with thanks, from the website of Keith Rogers of Mannum, South Australia at http://www.lm.net.au/~kerogers/ . We will refer to this as we go along. Notice that the three shapes are labelled A, B, and C.

Let's take a more careful look at the four prominent ferns mentioned above. We will start with A. australasicum, which is by far the most common in our local marketplace. This is a large fern with fronds to about 60 inches long and 8 inches wide. The fronds (lamina) are generally ovate and bright green, with tips being either rounded or pointed. The midrib has shape 'b' and the heavy 'keel' is easily felt. The sori are long and occupy at least half the distance from the midrib. This fern is native to Queensland and New South Wales in Australia, Norfolk Island, Lord Howe Island, New Guinea, New Caledonia, Fiji, Samoa, Tonga and Tahiti. It is somewhat cold tolerant so it grows here beautifully. In U.S. markets it almost invariably sold as Asplenium nidus, which it is not. I do not know of a true A. nidus in cultivation locally. A. australasicum is nearly always epiphytic, growing on the limbs and trunk of trees but it will occasionally be found on rocks or even in the ground when a mature plant has fallen. There is a variety that has lobed fronds and is known as A. australasicum ' Multilobum'.

As epiphytes, all of these bird's-nest ferns should be potted in a very coarse mix with great drainage. They should be under-potted to prevent accumulation of too much moisture although double-potting with the outer pot filled with gravel or the like may be necessary to provide a heavy enough base to support the large fronds. They should be lightly fed at frequent intervals during the growing season. They are very susceptible to snails and slugs and, in San Diego, also to the Giant White Fly.

As explained above, Asplenium nidus is the better known name locally. It is very similar in appearance to A. australasicum but with decided differences. For one, it is truly tropical and will not grow here without the protection of a greenhouse. It is native to northern Queensland in Australia, Christmas Island, east Africa and India. It is, in effect, Old World pan-tropical. The sori extend outward from the midrib but do not cover as much as half the distance to the margin. The most immediately identifiable feature is the shape of the midrib or cross-section that is as in 'a' in the figure with the strong 'keel' on the upper side. If you should acquire on of these plants and can give it the needed protection, you should otherwise treat it as for A. australasicum. Interestingly, there is a variety of A. nidus known as 'Plicatum' or more commonly as the 'Lasagna Fern' which is capable of living here unprotected and which may be found in the local marketplaces. It is much smaller with fairly narrow fronds which are heavily convoluted and pleated.

Asplenium antiguum is smaller that two above and does not form as tight a nest since the fronds taper toward both ends. It has a maximum frond length of about 40 inches and has narrower lamina to perhaps 4 inches. It has about the same hardiness range as A. australasicum but the cross-section of the midrib is different from both of the others having the shape shown in 'c' in the figure, i.e.; rounded both top and bottom. There is a very popular and handsome cultivar of this species that is produced by cloning at Santa Rosa Tropicals and is known as A. antiguum 'Victoria'. This form is fairly small and has many strongly ruffled laminae.

Since our introduction of Asplenium goudeyi to the U.S. market last autumn, we may consider it one of our basic bird's-nest ferns. It is smaller than the big epiphytes and is more often epipetric than epiphytic. It grows in fairly harsh conditions along the cliffs of Lord Howe Island and enjoys a marine atmosphere. Its fronds are stiff and greyish and fairly upright. It may be grown outdoors here in the same manner as A. australasicum.

While researching the information on these four species, I encountered a number of other bird's-nest type ferns that are seldom found in local cultivation, usually because they require special conditions. The following list is by no means exhaustive.

Asplenium cymbifolium. This tropical form from the Philippines, Indonesia, Borneo, Samoa and New Guinea is seldom if ever seen here. It has arching fronds that may be over a meter long and 10 inches wide. The frond bases are broad and dilated so that the rosette may even hold water. I have found no description of the midrib but it is probably shape 'b'.

Asplenium harmonii. This native of south-eastern Queensland is not a true birds'nest by my definition but is considered so by the Australians. It is seldom epiphytic, growing usually on basaltic cliffs, and the rhizome branches to form more than one growing point. The fronds taper to a narrow stem at the base. This results in a very untidy rosette that does not hold things well. Otherwise the plant is like A. australasicum.

Asplenium musifolium. Most modern authors give this plant specific status although some still list it as variety of A. nidus. The two are obviously very similar but A. musifolium has wider fronds to 10 inches and is a very dark green which A. nidus never is. Like A. nidus, this requires a greenhouse locally.

Asplenium phyllitidis. This is native to Singapore and Malaysia. It is similar to A. nidus (no mention of midrib) but has shorter and much narrower fronds that narrow at the base and form a rather poor nest. It is both epiphytic and epipetric and needs a very tropical environment.

Asplenium simplicifrons. This Australian native has long, narrow strap-like fronds with lamina up to 2 feet long and only about 2 inches wide. The midrib has shape 'b'. It is the most common bird's-nest in northern Queensland. It should make a good basket fern here if given even shade-house protection. There is a form which is sometimes called A. laciniatum, which is forked at the ends but this and also lobed forms occur naturally in the species

Asplenium serratum. This is the so-called American Bird's-nest Fern but it is only superficially so. It is native to the New-World tropics. It is epiphytic but, unlike the others, it has heavy, proliferous roots so that it spreads into many rosettes. It is like the A. nidus is appearance with fronds over three feet long and up to 6 inches wide but they are usually dull rather than bright green. The midrib is not described. The margins of the lamina are usually coarsely toothed. It would need protection to be grown here.

References:      

Goudey, Christopher J.A

Handbook of Ferns for Australia and New Zealand

Hoshizaki, Barbara Joe

Fern Growers Manual

Jones, David L.

Encyclopaedia of Ferns

Piggott, A.G.

Ferns of Malaysia in Colour

Mickel, J.T. & Beitel, J. M.

Pteridophyte Flora of Oaxaca, Mexico

Flora of Australia. Vol. 48.

Ferns, Gymnosperms and Allied Groups.

So, M.L.

Common Ferns of the Phillippines

Jones, David L.

Fern Society of Victoria 'Newsletter' Nov-Dec 1996. 
Reprinted from Muellaria Vol. 19, pp 37-40