The following is a list of some other Cyathea species that may prove reasonably viable in zone 9a or colder climates.  Please note that the majority of these are tropical to subtropical in origin and their cold-hardiness is vestigal; that is, they are significantly hardier than they would need to be to survive in their natural habitat.  To ensure their survival of winter cold, many of these should be kept rather on the dry side during frosts, and very well-insulated.  Only a few on this page do not fall into this category.

Cyathea aramagensis - information coming someday, maybe

Cyathea atrox (Papua New Guinea) - This moderate sized tree fern related to C. tomentosissima hails from monsoonal high mountain forests (to 11,000' elevation).  The trunk may reach a height of 18', with a 6" diameter; and the fronds seldom exceed 6' in length.  At these high elevations, temperatures typically stay within a range of 42°F and 62°F, with occasional subfreezing temperatures.  Freeze survival is aided by the fact that the temperature always rises above freezing during the day.  It is probably about on par with C. cooperi for hardiness, but it should be kept dryish in the winter to ensure frost survival.

Cyathea baileyana (Australia) - This species is called "Wig treefern" because the crown is covered in skeletonised base pinnules which look like a mass of hair.  It is rather slow-growing, but should be able to tolerate a few degrees of frost (probably around 27°F) and would be worth growing for the "wig."  The fronds can reach about 8', and the trunk eventually reaches about 10' tall.  Its introduction to cultivation may be slow since it is rather difficult to propagate.  Pictured in D. L. Jones' Encyclopedia of Ferns.

Cyathea brevipinna (Lord Howe Island) - Mainly for interest I am including this very intriguing species whose features are all compacted to make a squat little treefern with short, densely crowded fronds.  Perhaps even more baffling is the fact that no one has successfully raised these from spore, and in fact only one plant survives outside of its native habitat on a 2,600' high mountaintop on Lord Howe Island.  Once the secret to its successful cultivation is found (if it is ever found), it could certainly make quite a nice novelty item for collectors, and might grow well in full sun in such places as Great Britain and the extreme West Coast of the United States.  In my estimation it is likely that this species will tolerate a few degrees of frost, and its small fronds would make it easy to protect.  Pictured in D. L. Jones' Encyclopedia of Ferns.

Cyathea carascana (South America) - This speices grows in Andean cloudforests at elevations up to 14,000'--possibly the highest altitude of any tree fern.  It must certainly have some frost tolerance, but there is little information available about it.

Cyathea celebica (northern Queensland, New Guinea, Indonesia) - A very attractive species, whose 10' fronds take on a beautiful rigidity as they uncurl and expand, and whose stipes and upper trunk are covered in sharp black spines.  Although a dweller of cool highland rainforests, it is said to adapt to a wide range of climates, and is has even proven slightly frost-hardier than C. cooperi (guessing 25°F), and should certainly be grown in other parts of the world.  Closely related to C. leichhardtiana but more attractive and slightly faster growing.

Cyathea degaldii (Central America) - Hardy to at least 27°F.

Cyathea sp. 'floggacera'  - Hardy to at least 27°F.

Cyathea fulva (Central and South America) - A little-known dweller of Andean and Central American cloudforests as high as 14,000', along with C. carascana.  These are only two of many species from this region that would be worth trying for cold-hardiness.

Cyathea gleichenoides (Papua New Guinea) - A recently introduced species, this one grows at the incredible elevation of  12,400' where the usual temperature range is from about 37°F to 55°F.  In order to get enough warmth for adequate growth, the crown has a specialized heat absorbtion mechanism, and it grows mostly in sunny moist sites.  It typically inhabits open alpine grassland in the company of C. muelleri where frosts are common, some as severe as 18°F.  Interestingly, at this elevation the night temperature is significantly colder at ground level than several feet above ground, and the youngest plants are subjected to the worst of the frosts.  However, as with C. atrox, the daily temperature rise above freezing is crucial to frost survival, and I would not advise subjecting one to a severe frost unprotected in cultivation where freezes may persist for several days.  So far it seems very adaptable, tolerating a wide range of situations and climates.  Its cultural needs are probably similar to those of C. muelleri and C. tomentosissima.

Cyathea howeana (Lord Howe Island) - This robust tree fern grows an attractively scarred trunk to about 10' tall and 6" thick.  The soft, light bluish green fronds and attractively scarred trunk of this species make it a worthy subject for cultivation where a more imposing substitute for C. cooperi is desired.  It is similarly hardy (guessing 27°F), but may need a bit more heat than C. cooperi does to thrive.  In addition, the thick stipes and veins of the fronds make the uncurling croziers remarkably large, which is a stunning sight when all of them uncurl at once in the spring.  Pictured in D. L. Jones' Encyclopedia of Ferns.

Cyathea incisoserrata (Indonesia) - A rare, very beautiful species about which little is known.  The trunk is about 1' thick and may grow to a great height.  It is said to be hardy to 26°F, and therefore should be overwinterable in a zone 8b climate, but I would advise keeping it dry in the winter as with the other tropical latitude species.  Presumably it grows at a rather high elevation.

Cyathea kermadecensis (Kermadec Islands, 500 miles east of New Zealand) - A fast and easily grown treefern, rather delicate-looking, whose hardiness is also probably similar to C. cooperi (guessing 26°F).  It thrives in a sunny, humid situation, where it will develop an trunk up to 10' tall and about 4" thick, with an attractive crown of 6' long, dark green fronds.  The uncurling croziers and stipes are covered in light brown scales.

Cyathea lepifera (Taiwan, Phillipines, Japan) - The twisted uncurling croziers of this species have earned it the interesting common name of "Flying spider monkey tree fern."  The graceful, slender trunk, covered with scales near the crown, grows to a height of about 10', and the fronds generally reach about 8' long.  It is beautiful and easily grown in cool conditions, requiring only generous amounts of moisture to thrive, and probably tolerating a few degrees of frost.

Cyathea macarthuri (Lord Howe Island) - A large fern similar to C. australis and C. dealbata.  Exact hardiness unknown.

Cyathea macgregori (Papua New Guinea) - Grows at very high elevations with C. atrox, C. gleichenoides, and C. muelleri where it is subjected to some frost.  More information forthcoming.

Cyathea manniana (East Africa) - This large, coarse treefern is found in gullies at moderate elevations.  It is never found growing away from constant moisture and is probably quite cool-tolerant, but perhaps not very frost hardy.

Cyathea 'marleyi'  - A very large, robust tree fern with robust scales that is probably hardy to at least a few degrees of frost.  It was found in a nursery in Sydney, Australia owned by Judy and John Marley who are well known for their propagation of new and interesting species.  Its true genetic origin remains unknown, but it is now being propagated in England and Germany as well.

Cyathea mexicana (Mexico) - This species is reported as thriving in Rossdohan in southwest Ireland.  I suspect it is a cool cloudforest species with several degrees of frost tolerance.  I have not been able to find out much else about it.

Cyathea milnei (Raoul Island, New Zealand) - A species rather similar to C. dealbata, and likely to be suited to the same conditions, except that it comes from a more tropical climate.  The main difference is that it lacks the silvery undersides and stipes of C. dealbata, but it is a beautiful species nonetheless.  It has a slender, dark, rough trunk and glossy green, lacy fronds.  It may prove to withstand a few degrees of frost.

Cyathea muelleri (Papua New Guinea) - A little-known species from very high elevations (to 12,400') that grows with C. gleichenoides in open grasslands.  It should tolerate overnight frosts down to 18°F, but see C. gleichenoides (above) for more detalis.

Cyathea novae-caledoniae (New Caledonia) - This interesting treefern has a large swollen trunk base, appearing from a distance as if it has a butressed trunk.  It would probably tolerate a couple degrees of frost.

Cyathea podophylla (Taiwan) According to one source, this species has much more coarsely divided fronds than most Cyatheas resulting in a very different look (assuming the observed specimen was identified correctly).  Coming from Taiwan, it might be a little bit cold-hardy.

Cyathea princeps (Central America) - This vigorous species looks quite a bit like C. brownii.  Tolerates a few degrees of frost.

Cyathea thompsonii (East Africa) - This treefern comes from the same habitat as C. manniana.

Cyathea ursina (Central America)