This is the second in a series of posts exploring the mosses and liverworts (bryophytes) of Whiteknights campus. My first post covered epiphytic mosses and I promised there to introduce liverworts next. However, having found four more epiphytic mosses I have gotten myself much too excited to be able to finish with mosses just yet. Once these are off my chest I shall be able to get on with liverworts.
Three of the species are yet more Orthotrichum species, giving nine members of the genus on campus, seven on trees (the other two will be introduced in a future post describing mosses on stone). Such a number would be excellent for the best sites for bryophytes. Recalling, however, the sensitivity of epiphytes to pollution, for an urban park nine Orthotrichum species is superlative! Having exhausted the widespread species I don’t expect to find any more. I should like to emphasize that several of the epiphytic mosses discussed in these posts are formerly of very rare occurrence in Berkshire, the eastern part especially. See Bates’ Bryophyte Flora of Berkshire, 1995, in which, for example, O. striatum, is considered as possibly extinct.
Syntrichia papillosa has the tongue shaped leaves and long pointed tip of other members of the genus. The incurved leaves (not terribly well illustrated here, see the BBS guide) and the bunch of gemmae are unique features. Image by D. Morris
Rather than look at these first, I shall offer the reader some respite from Orthotrichum and introduce a member of a very different order of mosses, the Pottiales. This is a large group of very often weedy mosses and we shall meet many more in the course of this series. Syntrichia papillosa is among the small number of epiphytes in the order. Like many of the epiphytic mosses and liverworts in these posts, it is another species that appears to be spreading with improvements in air quality. Most records are scattered across southern England, but it is uncommon (this is the first time I’d seen it). It was formerly relatively widespread on elms in Berkshire, until mature trees were killed off by Dutch elm disease.
This species looks broadly like the Syntrichia species to be met with in future posts, but two characters are diagnostic. First, the leaves curl strongly inwards, an uncommon state (more usually the leaves of mosses curl downward). Second, there is a cluster of bright green rounded gemmae toward the end of the leaf. Gemmae (singular: gemma) are asexual propagules that can be broken off and dispersed (by birds and insects?) to germinate and found new colonies that are clones of the parent plant. Like many mosses that have gemmae, S. papillosa is not known to reproduce sexually in the UK, i.e. capsules have never been seen here. In situ this is a very beautiful little plant, growing in small bright green colonies, each plant a half centimetre or so wide and a little less in height.
Now to return to Orthotrichum. O. striatum and O. lyellii are both robust species with some resemblance to O. affine, the former especially. O. lyellii, however, is probably one of the simplest epiphytic mosses to identify, for although it rarely produces capsules the upper leaves are covered in a brown haze of gemmae. Although large like O. affine, O. lyellii is usually a little taller and forms looser patches with what can be best described as a leggy appearance. I find that this jizz is sufficiently characteristic to allow me to spot this species growing amongst other epiphytes from a short distance.
The characteristic brown fuzz (left) of Orthotrichum Lyellii. Right: a close up showing the brown gemmae clothing the upper leaves. Images by D. Morris
O. striatum is very similar to O. affine and can only be separated during winter and spring when its capsules are in good condition. However, if you are familiar with O. affine then the differences really jump out at you under a hand lens, the teeth at the mouth of the capsule (peristome) especially. The capsule of O. affine has eight teeth which are bent all the way back from the mouth to lie flat against the capsule (reflexed), while O. striatum has twice as many and these are bent at right angles (patent). The capsule also lacks the obvious furrows present in almost all other Orthotrichum species (see e.g. the image of O. stramineum below) and the calyptra is markedly hairy. If you are particularly observant, you will notice a set of inner teeth at the mouth of the capsule (endostome) absent in O. affine, and the leaves are also more pointed.
Orthotrichum striatum. Left: ripe and ripening capsule. Unlike most other species the capsule is conspicuously smooth. Like O. affine, it is also one of a small number of species in the genus in which the stomata of the capsule (right) are superficial, i.e. not obscured by cells above it. Images by D. Morris
The final species of Orthotrichum is of a similar size and habit to O. pulchellum, growing in neat cushions to 1cm tall. When in season these cushions bristle with capsules with characteristically red-tipped calyptrae. When the calyptra is shed and the capsule dries, it is strongly contracted below the mouth and resembles a flask. In addition to these characters (which might not be present simultaneously), this is the only Orthotrichum species in which the base of the seta is surrounded by long silvery hairs like those found on the calyptra.
Orthotrichum stramineum. Left: the characteristic red-tipped calyptra. Right: the unique hairy base to the seta. I couldn’t get photographs to beat these from the Essex Botany and Mycology Group.
If you wish to see any of the mosses discussed so far in this blog in their natural habitat, then I have found that they are all present on one of the horse chestnuts by the pond in the Harris Garden. Although she took our botany class to this tree to examine its lichens and not bryophytes, I am very grateful to Fay Newbury for having this tree and its bounty brought to my attention! All the Orthotrichum species can be seen elsewhere on campus but it is the only place where I have found them growing together and the only tree I know for Syntrichia papillosa. It is also a good tree for lichens.