J Hattori Bot. lab. No. 84: 37-47 (July 1998) THE ARCHITECTURE OF THE LEMBOPHYLLACEAE (MUSCI) R. S. TANGNEY1 ABSTRACT. An analysis of the architecture of the Lembophyllaceae is presented and its value in the taxonomy of the family is assessed. The Lembophyllaceae produce a variety of growth forms, rang­ ing from creeping mats to loose erect-ascendant wefts and pendant fronds. Characters of stem orien­ tation, branching, rhizoid distribution, leaf orientation, size and shape, and the production of determi­ nate or indeterminate growth are used to describe merophyte development. Variation in the pattern of merophyte development yields an architectural pattern common to taxa, and the genera differ from each other in their relative expression of this pattern. The same architecture is therefore seen to un­ derlie the various growth forms exhibited. K EY WORDS: mosses, Lembophyllaceae, architecture, ontogeny, heterochrony. INTRODUCTION The Lembophyllaceae are a Southern Hemisphere family of pleurocarpous mosses, occurring in Australasia and southern South America. During its history, the family has in­ cluded a diversity of unrelated elements that in recent years have been transferred to other families (Buck 1980, 1994; Vitt 1984; Crum 1991 ; Tangney 1996, I 997b ). While the fami­ ly recognised in a more restricted sense (than that, for example, of Brotherus 1924- 25) is morphologically more coherent, there remain difficulties in the separation of the genera. These problems are related to the extreme variability of species in the family. This plastici­ ty is associated with variation in the underlying architecture (Tangney 1996). This descrip­ tion of the architecture aims to provide a basis for the understanding of the variability of the species, as well as the inter-relations of the genera. ARCHITECTURE AND GROWTH FORM. The term architecture is not generally used in reference to bryophytes. Rather, the cat­ egories of growth-form and life-form have traditionally been employed to describe the morphological aspects of branching pattern and overall appearance (physiognomy) of bryophytes, respectively. While there is a clear difference in the definition of these terms, their usage has been ambiguous and the value of growth-form in morphological analysis has been eroded. Magdefrau (1982) considered growth-forms to be the" ... genetically fixed method of ramification'', i.e., characteristic of an individual, and life-forms to be an " ... as­ semblage of individuals and growth-form, modified by external conditions'', i.e., character­ istic of a group of individuals. Growth-form is therefore subordinate to life form as it is a component of the latter. While the distinction between the two categories is clear, the use of the terms has been confusing. For example, Magdefrau (1982) cited earlier authors' defi­ nitions of growth form as being strictly morphological, yet considered growth form to be modified by the external environment. 1 Department of Botany, University ofOtago, P 0 Box 56, Dunedin, New Zealand. 38 J. Hattori Bot. Lab. No. 84 I 9 9 8 Gimingham and Robertson (1947) produced a growth-form classification based on that of Meusel (1935). Their modifications to Meusel's detailed system explicitly gave more importance to "general growth morphology" than to branching pattern. Thus their 'growth form' became an index of environmental influence rather than genetically fixed. Therefore, both life-form and growth-form systems have come to produce very simi­ lar classifications, even sharing descriptive terms, for example turf, weft, cushion and mat (see Magdefrau 1982 and Richards 1984). This, coupled with the environmental influence associated with growth-forms, has led to a perception that characters of the growth-form have little value in taxonomy. Because of the ambiguity surrounding growth-forms, the term architecture, as applied to vascular plants, is preferred. Both Mishler and De Luna ( 1991) and La Farge-England (1996) have shifted the emphasis of growth-form study back to an architectural analysis. The architecture of a plant is the result of meristematic activity, a developmental sequence which is independent of physiognomy, biological type or taxonomic position (Halle and Oldeman 1975). The use of the term architecture emphasises the analysis of the develop­ mental branching pattern rather than overall appearance (Mishler and De Luna 1991 ). Bryophytes may therefore exhibit similar architectures to other groups of plants, and differ­ ent 'growth-forms' may be produced by similar architectures. Mishler and De Luna ( 1991) outlined a hierarchical framework for ontogenetic de­ scription ofbryophytes. It utilises some terminology applied to vascular plants and consists of five hierarchical levels of development; the cell, the metamer (=the merophyte), the module (=the branch), the branch system (=the shoot), and the shoot system. Differentia­ tion occurs at each level and may vary within each level depending on the developmental level of the higher stage. For example, merophyte development may vary both within a branch and between branches of the same shoot. The pattern of merophyte development and the timing and pattern of the structures produced, therefore yields an architectural pat­ tern that may be used to compare taxa. THE LEMBOPHYLLACEAE The Lembophyllaceae are characterised by morphological variation within taxa such that no characters are discontinuous between the genera. Dixon ( 1927) considered that the species were easy enough to recognise, but that the genera were not. For example, Camp­ tochaete exhibits frequent variation on its dendroid-stipitate architecture. This flexibility of form, combined with vigorous growth produces plants that blur species boundaries. Some of these forms (called 'deflexa' forms by Dixon, 1927) have been a source of superfluous names, and previous authors have noted taxonomic difficulties associated with variability (Dixon 1927, Sainsbury 1955, Scott and Stone 1976, Crum 1991 ). This variability is a function of plant architecture (Tangney 1996), and this explication of the architecture and variation of the Lembophyllaceae is aimed at an understanding of the variation observed. In pleurocarpous mosses, growth of the apical cell is not terminated by gametangial production, i.e. module growth is not determinate as in acrocarpous mosses. Therefore, there is the potential for greater differentiation within modules. In this analysis, characters are utilised as indicators of merophyte development within the levels of module and branch R. S. TANGNEY: Architecture of the Lembophyllaceae 39 system (shoot). This pattern ofmerophyte development is used to compare the taxa. Characters utilised: Stem orientation Orthotropy: growth mostly erect with radial symmetry Plagiotropy: growth mostly horizontal with flattened (complanate) growth Branching (presence or absence) Growth Monopodial: the continuous activity of a single apical cell. Sympodial: growth from lateral apical cells. For example, when growth of the frond axis api­ cal cell stops, growth of new modules, comes from lateral apical cells. Growth Determinate: Growth producing a fixed structure or number of structures only, e.g. a leaf, a sporophyte, or a branch of fixed length. Indeterminate: Growth producing a succession of structures of no fixed number, e.g., the main axis of a pleurocarpous moss. Rhizoid distribution Leaf orientation, size and shape DESCRIPTION OF TAXA Camptochaete exhibits a diversity of architectural pattern which encompasses that of the other genera. Camptochaete is described in detail, and the other genera are compared to it. The genera are seen to differ from each other in the relative expression of the same un­ derlying pattern. Observations are based on studies of herbarium, field, and cultivated ma­ terial. Camptochaete Reichdt. Ten species in two sections (Tangney l 997a). Details of the archi­ tecture of the two sections differ. The architecture of species in Sect. Camptochaete is de­ scribed, and differences with sect. Thamniella are noted below. Camptochaete sect. Camptochaete Growth form (Fig. 1.). Plants are erect-ascendant, forming loose wefts, and occasion­ ally, distal stems and branches may be pendant. Rarely, plants are found in unattached loose-lying "moss-balls" on the forest floor. Stem differentiation present. Erect stems are produced from creeping stolons. Stems consist of a lower unbranched stipe and an upper branched frond. Stolon growth is pla­ giotropic; creeping with rhizoids scattered. Leaves erect and imbricate, often erose. Stipe growth is orthotropic, developed from the creeping stolon by the stolon tip becoming erect. Leaves of the stipe are erect and imbricate. The stipe is usually unbranched and rhizoids are absent. Fronds are plagiotropic; with irregular bi-tripinnate branching usually produc­ ing flattened fronds. Fronds are determinate, with lateral branches determinate and the frond axis also usually determinate. Reiteration. Reiteration of the branch system occurs either sympodially or monopodi­ ally. Sympodial innovations arise as lateral branches from the base of the stipe, and are ini­ tially plagiotropic (stolon), become orthotropic (stipe), and then plagiotropic (frond). 40 J. Hattori Bot. Lab. No. 84 I 9 9 8 Camptochaete a Fig. I. Architecture of Camptochaete. a. stolon, b. stipe, c. frond, d. stoloniferous or flagelliferous growth of the frond, e. elongate or 'deflexa' form. Growth of module a-b-c is monopodial. Reiteration is either sympodial or monopodial at d., or sympodial