J. Hattori Bot. Lab. No. 76: 13- 20 (Oct. 1994) ON THE EVOLUTION AND CIRCUMSCRIPTION OF THE NECKERACEAE (MUSCI) JOHANNES ENROTH 1 ABSTRACT. The family Neckeraceae (Musci) contains the traditional subfamilies Neckeroideae and Thamnobryoideae ("Thamnioideae"). The family must be defined mainly on gametophyte characters, since the sporophytes display great plasticity. A few gametophyte characters critical in the definition of the Neckeraceae are pointed out. A list of the 23 genera provisionally accepted in the family is provided. The key word in understanding the evolution of the Neckeraceae is reduction, implying anatomical and morphological reduction in both generations. For example, the evolution of the peri­ stome shows a reduction series from the generalized perfect hypnoid type (e.g., Thamnobryum Nieuwl.) to various reduced "neckeroid" types (e.g., Neckera Hedw. and Neckeropsis Reichardt). Several primitive versus advanced character states in the gametophytes and sporophytes of neckera­ ceous mosses are briefly discussed. Hypnodendron (C. Mull.) Lindb. ex. Mitt. and Climacium Web. & Mohr. are provisionally recognized as outgroups. It is emphasized that the evolution of the two gener­ ations have not always progressed at same "rate", since there exist genera with a primitive gameto­ phyte and an advanced sporophyte, and vice versa. INTRODUCTION To understand the present-day expression of a given natural group of organisms, one must have a good comprehension of the group's evolutionary history. This paper presents, for the first time, ideas on the evolution and their bearing on the circumscription of the iso­ bryalian moss family Neckeraceae. The generic relationships within the Neckeraceae have not yet been cladistically scrutinized, and global revisions are wanting for some critical genera, such as Neckera Hedw., Porotrichum (Brid.) Hampe, Porotrichodendron Fleisch., and Thamnobryum Nieuwl. Much work thus remains to be done on the family, and the present paper may be viewed as a concise introduction to a forthcoming generic revision by the author. This paper discusses several primitive and advanced character states encountered in the gametophytes and sporophytes of the neckeraceous mosses. The genera Hypnodendron (C. Mull.) Lindb. ex Mitt., monographed by Touw (1971), and Climacium Web. & Mohr (cf. Horton & Vitt 1976) are recognized as possible sister groups of the Neckeraceae, which is important to note regarding the polarization of the character states. The Necker­ aceae includes the traditional subfamilies Neckeroideae and Thamnioideae ( = Tharnnobry­ oideae, cf. Ochyra 1986). The subfamily Leptodontoideae was recognized as an indepen­ dent family, the Leptodontaceae by Buck (1980), Buck and Vitt (1986) and Enroth (1991); an attempt to elaborate the circumscription of that family will be presented in a forthcom­ ing paper by the present author. 1 Department of Botany, P.O. Box 7, FIN-00014, University of Helsinki, Finland. 14 J. Hattori Bot. Lab. No. 76 I 9 9 4 ON THE EVOLUTION OF THE NECKERACEAE The key word in understanding the evolution of Neckeraceae is reduction, that is, anatomical and morphological reduction in many structures of both generations. It is clear that the evolution of one generation has not always "kept pace" with that of the other. The following examples represent genera whose generations differ strongly in their "evolution­ ary stages" (cf. Table 3). I) Pinnate/la Fleisch. and Curvicladium Enroth, two closely related genera (Enroth 1993), have primitive gametophytes resembling those of Thamnobryum. The sporophytes, however, are relatively advanced; the peristomes are hardly distinguishable from those of Himantocladium (Mitt.) Fleisch. and many species of Neckeropsis Reichardt. 2) The monotypic Hydrocryphaea Dix. has a fairly primitive, "thamnobryoid" ga­ metophyte (cf. Manuel 1975), but the sporophyte is highly advanced. The capsule is im­ mersed among the large perichaetial leaves, and the peristome is strongly reduced, with short, smooth exostome teeth, and filiform endostome segments. The sporophyte is proba­ bly adapted to the rheophytic habitats (in flowing water) favoured by Hydrocryphaea. 3) The sporophyte of Pendulothecium Enroth & He is primitive and comparable with that of Thamnobryum. The gametophytes are more advanced: a central strand is lack­ ing from the stems, only few well-differentiated stipe leaves are present, and the costa is weaker and shorter than in Thamnobryum. 4) The advanced gametophytes of the monotypic genera Baldwiniel/a Broth. and lsodrepanium (Mitt.) Britt. bear a strong resemblance to Neckera, but the sporophytes, with hypnoid peristomes, are much more primitive. These examples point out that a "thamnobryoid" gametophyte can be combined with a "neckeroid" sporophyte, and vice versa. This has an important corollary regarding the de­ marcation between the Neckeraceae and the Thamnobryaceae ~ namely that there is no such a demarcation. This was also the opinion of Fleischer ( 1908): "Eine bis in die Gegen­ wart <lurch alle Dbergangsformen erhaltene, liickenlose Formenreihe ist diejenige, welche von Neckera iiber Pinnate/la und Porotrichum zu Thamnium fiirht, so dass diese unwider­ leglich geschlossene Formenreihe als Familie festgehalten werden muss". Some genera (e.g., Thamnobryum) are clearly more primitive than others (e.g., Neckera), but they repre­ sent a single family, the Neckeraceae. If the traditional (Brotherus 1925) concepts of the subfamilies Neckeroideae and Thamnioideae are retained, the former is generally clearly more advanced than the latter. Future cladistic work will show whether the traditional sub­ division can be retained. Gametophyte generation (Table 1). The branching and stem structure are discussed in the chapter dealing with the cir­ cumscription of the Neckeraceae. The other characters in Table 1 are discussed here. Sexuality - The primitive state is dioicous, and the advanced state is autoicous or syn­ oicous. There are a few exclusively dioicous genera, such as Porotrichum, Homaliodendron Fleisch., and Pinnatella. It is clear that the change in sexual condition has occurred more than once. Examples of genera with dioicous and autoicous or synoicous species include Thamnobryum, Himantocladium, Neckeropsis, and Neckera . J. ENROTH: Neckeraceae (Musci) 15 Table 1. Some primitive and advanced character states in the gametophytes ofneck­ eraceous mosses. See text for discussion. Primitive Advanced Sexuality dioicous autoicous (syn-) Branching (sub )pinnate, ±dense irregular, remote Stem structure central strand diminutive central strand none Stipe leaves numerous well-differentiated few well-differentiated not overlapping overlapping Leafposture "octastichous" complanate Leafsy mmetry symmetric asymmetric Leafapex serrate serrulate teeth composite teeth not composite Costa strong, long, single weak, short, double abaxial teeth present smooth Leaf cells relatively short more elongate moderately incrassate strongly incrassate walls± solid walls porose inframarginal inframarginal limbidium present limbidium none Stipe leaves - The primitive taxa mostly have numerous well-differentiated stipe leaves which are not overlapping. However, the changes to the advanced states have taken place independently in a few genera, since species of the primitive type and advanced type are present in Thamnobryum and Pinnate/la, for example. Leaf posture - The primitive state is only superficially "octastichous", because the leaves are basically spirally arranged and apparently the most common phyllotaxy is 3/8. Genera such as Neckeropsis, Homalia (Brid.) B.S.G., Homaliadelphus Dix. & P. Yarde, as well as many species of Neckera, have the advanced complanate leaf posture. Thamnobryum, for instance, has species of both types. Leaf symmetry - This character is apparently connected with the preceeding one, since plants with an "octastichous" leaf posture mostly have rather symmetric leaves, while species with a complanate foliation have distinctly asymmetric leaves. Leaf apex - The primitive serrate condition with large, composite teeth is encountered in most species of Thamnobryum, Porotrichum, Porothamnium, and Homaliodendron, as well as in the monotypic Curvicladium. Serrulate apices with small teeth is by far the more fre­ quent condition in the more advanced genera. Costa - A primitive neckeraceous costa is single, strong, and vanishes just below the leaf apex, as in Thamnobryum and Pinnate/la. The presence of abaxial teeth is interpreted as a primitive condition, since it is encountered in the tentative outgroups Hypnodendron and Climacium. The advanced, short, weak, often double costa is present in many species of Neckera, and a costa is highly vestigial or absent in Homaliadelphus. Leaf cells - A primitive neckeraceous leaf cell is relatively short, moderately incrassate, 16 J. Hattori Bot. Lab. No. 76 I 9 9 4 Table 2. Some primitive and advanced character states in the sporophytes ofnecker­ aceous mosses. See text for discussion. Primitive Advanced Seta long short Capsule asymmetric symmetric horizontal-pendulous erect Stomates phaneropore none Annulus differentiated none Exostome teeth shouldered not shouldered cross-striolate papillose or smooth trabeculae projecting not projecting Endostome segments fenestrate perforate or filiform strongly keeled slightly keeled Basal membrane high low Cilia well-developed rudimentary or none and has solid walls. Longer, strongly incrassate cells with porose walls are advanced. Ho­ moplasious, and possibly also reversed,