The leafy liverwort Lophozia herzogiana gives an example of how new evidence can change bryogeographical views, in this instance going from what seems a highly plausible hypothesis back to a more open question.
The species was first described in a paper published in 1962 and the description was based on material collected by the New Zealand bryologist KW Allison near Atiamuri, itself near Rotorua in the North Island of New Zealand. While this species was published in 1962 Allison's collections were much older and he had in fact collected this liverwort a number of times in the Rotorua area between 1929 and 1940. He'd mostly found it short Manuka (Leptospermum scoparium) on decaying tussocks, soil or rotting logs but it also grew "on vegetation in swamp" and "on dead tutu (Coriaria) in opening in pine forest". For a long time the Rotorua area was the only known location for this species. On the basis of that fact it would be natural to wonder if the species were endemic to New Zealand. The liverwort has not been collected from the Rotorua area since Allison's time and much of its habitat is now pine plantation.
In 1986 Lophozia herzogiana was collected in Woolmer Forest in the county of Hampshire in southern England. Two such widely separated locations naturally prompted more questions about this liverwort's distribution and, in a paper published in 1989, two British bryologists (AC Crundwell and AJE Smith) assessed some possibilities. There are various well-studied bryophytes which are found naturally in both the more northern parts of the Northern Hemisphere as well as the more southern parts of the Southern Hemisphere, but not in between. This is called a bipolar distribution. Crundwell & Smith noted that the other species of Lophozia that were classified in the same sub-genus as Lophozia herzogiana were mostly confined to the Southern Hemisphere, there being just one exception. The two bryologists next looked at the family Lophoziaceae, which contains Lophozia and closely related genera. Within this family there are a few cases of species with bipolar distributions, so Lophozia herzogiana might be a native British species. The Hampshire habitat in which Lophozia herzogiana occurred was a Callunetum, which is the term for an area dominated by the heath Calluna vulgaris. The Callunetum in question was well away from houses and gardens but could only be regarded as semi-natural since it was maintained by relatively frequent fires, mostly started by humans, which prevented invasion by birch, oak and pine. After a fire the area would be more easily colonized by propagules introduced from outside.
The area of Hampshire in question is fairly rich in bryophytes, but is not renowned for bryological rarities. That observation does not rule out the case for native status for Lophozia herzogiana. However, if the area contained a number of unusual species the case would be stronger. The argument would then be that the area is a refuge for complex, native bryophyte communities that have disappeared from other areas through changes in land use.
Crundwell & Smith considered that there was a stronger case for the species being introduced to the area. Moreover, as it had not been recorded from anywhere else in Britain, they concluded it was likely the species had been introduced from overseas. There seemed to be two possible ways in which that could have happened.
The area is within Ministry of Defence land and the area has been military land since the 1860s. During the second world war many overseas troops were stationed in the area – perhaps including New Zealanders who could accidentally have introduced the liverwort, perhaps with their equipment. Crundwell & Smith did write that "... with the army obsession with 'spit and polish' this is only a remote possibility...".
The Lophozia site in Woolmer Forest was only two kilometres from Blackmoor Estate where wool waste (or wool shoddy) had been used as fertilizer. In 1974 a survey of the grasses at Blackmoor revealed the presence of over 200 alien species, about half being Australian species. It is likely that many grass seeds travelled to Blackmoor with Australian wool or wool waste, but Lophozia herzogiana is not known from Australia. New Zealand was a significant supplier and in the period 1948-1951 New Zealand supplied about a quarter of the wool imported into Britain. A somewhat cursory search through some literature about New Zealand grasses shows that at least a few of those Australian grass species had also been known from New Zealand before the 1950s. This gives some support to the idea that Lophozia herzogiana travelled to Blackmoor in New Zealand wool or wool shoddy, though there is no direct proof of New Zealand material being used at Blackmoor. There is no Callunetum on the Blackmoor Estate, according to Crundwell & Smith, there was much suitable Lophozia herzogiana landscape between Blackmoor and Woolmer Forest. If the liverwort had been deposited in the Blackmoor grounds it could have travelled from there to Woolmer in a number of small steps, rather than having had to do so in one long leap.
While Crundwell & Smith knew of no definite cases of bryophytes introduced on wool shoddy they also commented that areas where wool shoddy had been in use had not been searched for bryophytes. The authors finished by commenting that the New Zealand-to-England hypothesis was a distinct possibility but that to give it more support there'd need to be a study into how long spores, gemmae or plant fragments remained viable.
In the late 1990s Lophozia herzogiana was found at another site within Woolmer Forest. Incidentally, before the second find it had been thought that the liverwort had been eliminated from the original Woolmer site through conservation measures. The elimination occurred during the excavation of a silted pond, part of a recovery program for the Natterjack Toad. The excavation debris had been dumped unintentionally onto the original Lophozia area.
As you can see the bryologists Crundwell and Smith put in a fair amount of non-bryological research in order to produce a plausible explanation for the occurrence of Lophozia herzogiana in Britain. This account gives you a good idea of the sort of work that might be needed in a bryogeographical investigation. Not only must likely avenues be followed but even some unlikely avenues must be investigated in order to produce good evidence of their unlikeliness. Even after all their work, Crundwell & Smith could produce only a "plausible but not proven" scenario. But that's typically the case in many bryogeographical arguments.
During a British Bryological Society excursion in 2004 Lophozia herzogiana was found growing on Sphagnum contortum at Mortlach Moss, a bog in Aberdeenshire in northern Scotland. That was a quite different habitat to that in Woolmer Forest. The Scottish site was also an unspoilt area, far from human influence, which prompted some to wonder if the species were in fact naturally in the British Isles and at additional sites between the two known locations. Perhaps, instead of introduced to Britain, it had in fact been introduced to New Zealand.
You might wonder if Lophozia herzogiana is in fact more widespread in the United Kingdom but easily confusable with some more common and better-known species. If that were the case it could be that Lophozia herzogiana has been seen, and even collected, many times but on most occasions has been written of as that other liverwort. It's a fair question and it is impossible to prove that Lophozia herzogiana has never been mistaken for some common species, but there are two facts that argue to the contrary. The first is that Crundwell & Smith wrote "Lophozia herzogiana is unlikely to be mistaken for any other British liverwort..." and then noted some of its distinctive features. The second is that there is a sizeable, active and highly knowledgeable community of professional and amateur bryologists in the United Kingdom. So mis-identification seems impossible but there is still the possibility that the species is more widespread in the United Kingdom, since the country still contains some poorly explored areas, bryologically speaking. In fact members of the British Bryological Society visited North Aberdeenshire in 2004 precisely because it was such an area.
A liverwort specimen collected in Australia in 1993 was identified as Lophozia herzogiana in 2006. This specimen was collected in the Tinderry Mountains of New South Wales, near Canberra. The collection site was an open eucalypt woodland with tall shrub understorey and the liverwort was growing on leaf litter under grasses, sheltered by shrubs. While undoubtedly Lophozia herzogiana, the Tinderry collection shows some differences from the Rotorua material. It is also possible that a relatively recent specimen collected in the South Island of New Zealand is also Lophozia herzogiana, but it shows some differences from the North Island specimens.
The additional Australian and New Zealand have put the species back into the puzzle category. Have humans carried it from one hemisphere to the other? Is it a bipolar species? Is it in fact more widely distributed between Australasia and the United Kingdom? There the matter stands. It is clear that the discovery of this species at more locations would help greatly. There is also the thought as to whether DNA analyses could throw some light on the relationships between the different colonies.