l

THE

AUSTRALIAN

• VASCULAR EPIPHYTES •

FLORA & ECOLOGY

by Benjamin John Wallace

Thesis submitted for the degree of Doctor of Philosophy of the University of New England, NSW. Botany Department December 1981 ------··-· ,_ ~ .. -- .·:._:.> ...::'~--.-~,

This work I dedicate to my father, Robert, who gave so much to his children and who urged me to continue my formal education as far as possible. Also, without my inheritance of his doggedness, this work would surely have foundered. Vascular epiphytes of a Ficus watkinsiana: a semi-schematic summary of distribution; Derrigo National Park, NSW. See also p. 109 and p. 188 for fuller explanation. -·~----~------~· ------·----·- ·------·-·-·----~---·------

i

Acknowledgements

There is quite a number of people whom I wish to thank for their assistance, without which, this project would have been very much more difficult, if not impossible.

Foremost is Professor {now Emeritus) Noel C.W. Beadle, who in the first place assisted my entry into the Faculty of Science, which eventually led to the present work. During my postgraduate career he was my chief mentor and supervisor and I am grateful for this and particuarly for his allowing me to follow the projects of my ow~ interest. Even in his retirement he offered advice and critically read some of the manuscript of this dissertation.

I am also considerably in debt to my present supervisors, Mr John Williams and Dr Jim Charley, not only for their advice, criticism and encouragement but also for the example of their academic astuteness and leadership.

To Dr Klaus Winter I owe a great deal for his prompting, advice and general facilitation of the work on CAM, which forms a crucial part of my thesis. He was very generous in allowing me to use the results of the CAM survey which he conducted, in his critical reading of the relevant manuscript and in offering encouragement and moral support when needed. Professor Barry Osmond also read this section and gave advice as well as having some o13c ratio determinations done for me.

The staff of the CSIRO Forest Research Station, Atherton were helpful in various ways on my trips to north Queensland, particularly Messrs Geoff Stocker, Bernie Hyland, Alick Dockrill and Bruce Gray. The Stockers took me into their home while I recovered from the effects of scrub typhus.

The staffs of the herbaria of both Sydney and Brisbane were very co~operative in providing access to specimens and to literature in their libraries as well as offering advice and encouragement.

Mr Jack Sewell allowed me free access through his property to the Long Point study site and Messrs Cliff Faint and Mike Saunders provided me with rainfall data for that area. ii

Messrs Keith Ingram, Don Blaxell, Ken Hill, Dick Windsor and Dr Col Bale all assisted by critically reading manuscript and offering encouragement generally.

The co-operation of the NSW and the Queensland National Parks and Wildlife services must be acknowledged. The Australian Orchid Foundation provided financial assistance for a field excursion to Cape York.

To my wife, Irene, I owe much for her patience and forbearance over the years of this project, particularly the last one,and also for typing up sections of the manuscript. Margaret Henderson also typed part of the manuscript.

Jenny Worgan typed most of the manuscript and compiled the Table of Contents, Lists of Tables, Figures and Plates. Her efficiency, cheerfulness and understanding helped considerably.

Many other friends and my family gave various forms of assistance and encouragement and my thanks go to them also.

Lastly, but certainly not least, I would like to thank the technical staff of this Department who assisted in various ways, particularly Gordon White whose unstinted co-operation and resourcefulness was well appreciated.

Statement of Originality

I certify that the substance of this dissertation has not been submitted for any degree and is not being currently submitted e+sewhere.

Also, all of the work recorded herein is my own except as otherwise acknowledged.

Signed

Date

j iii

CONTENTS

Acknowledgements List of Tables vii List of Figures ix

List of Plates X List of Abbreviations xi Abstract xii

General Introduction 1

CHAPTER 1: LITERATURE REVIEW &EPIPHYTE CLASSIFICATION 4 1.1 Review of selected, relevant literature 5

1.2 Epiphyte classification and terminology 11

1.3 Glossary of important and miscellaneous terms 18

CHAPTER 2: THE AUSTRALIAN VASCULAR EPIPHYTES 22 2.1 Introduction 23

2.2 Materials and methods 25

2.3 Results 25

2.3.1 Vascular epiphyte flora list 25

2.3.2 Accidental epiphytes 46

2.3.3 Facultative terrestrial/lithophyte/low epiphyte 47 spp.

2.3.4 Synopsis of Australian vascular epiphyte flora 49 - taxonomic group strengths - main geographic distribution patterns - life form groupings - physiognomic type etc - exposure preference index - occurrence of CAM - disseminule type groupings

2.4 Discussion 51

2.4.1 General considerations 51

2.4.2 The groups 51 iv

2.5 Biogeography of the Australian vascular epiphytes with 59 particular reference to the

2.6 Myrmecophilous epiphytes in 66

2.7 Conclusions 68

CHAPTER 3: EPIPHYTE ENVIRONMENTS IN AUSTRALIA 70

3.1 Introduction 71

3. 2 Materials and Methods 72

3.3 Results 73

3.3.1 Contin~ntal distribution of rainforest, MAR 73 and average annual potential evaporation

3.3.2 Macrovegetation profiles 74

3.3.3 The study sites 76

a. Subtropical Rainforest, Dorrigo NP, NSW 76 b. Littoral Rainforest, Shelly Beach, 79 Port Macquarie, NSW c. Dry Rainforest, Long Point, Hillgrove, NSW 82 d. Warm Temperate Rainforest, Hmnber Hill, 84 New England NP, NSW e. Cool Temperate Rainforest, Wrights Lookout, 87 New England NP, NSW f. Semi-evergreen Mesophyll Vine Forest, Leo Ck,80 Mcilwraith Range, Qld

3.4 Discussion 90

3 .4.1 Geography of epiphyte environments in Aust. 90

3.4.2 The study site macroenvironments 92

3.4.3 Macrocorrununity structure 93

3.4.4 Microhabitat physical factors 95 - Irradiance 95 - maximmn and minimtnn air temperatures 95 - frequency of precipitation 96 - air movement 96 - air evaporative power 97

3.5 Conclusions 97

3.6 Recommendations for future investigation of epiphyte 98 microclimate V

CHAPTER 4: SYNECOLOGY OF EPIPHYTES 99 4 .1 Introduction 100

4.2 Synecology of the Australian epiphytes 103

4.2.1 Introduction and aims 103

4.2.2 Materials and methods 104

plot location and size - phorophyte table - epiphyte table - distribution charts - phorophyte/epiphyte transect profiles

4.2.3 Results 106 Plot 1 STRf, Dorri go NP 106 Plot 2 LRF, Shelley Beach 110 Plot 3 DRf, Long Point 113 Plot 4 WTRf, Humber Hill 116 Plot 5 CTRf, Wrights Lookout 119 Plot 6 SEVF, Leo Creek 121

Summary of phorophyte & epiphyte parameters 125

4.2.4 Discussion 126 A. The phorophytes 126 B. The epiphytes 126 1. Floristic diversity 126 2. Population densities 127 3. Structural complexity of epiphytic 129 vegetation a. zonation 129

b. physiognomic types & life forms 131

C. Epiphyte-phorophyte relationships 133 4. Specificity 133 5. Epiphyte-bearing ability of phorophytes 136

i. phorophyte axeny & epiphyte pronenessl36 ii. epiphytes and allelopathy 138 iii. phorophyte size/age effect 141

4.3 Summary of epiphyte synecology discussion 146

4.4 Nest-epiphyte communities and succession 148 vi

CHAPTER 5: EPIPHYTES AND CRASSULACEAN ACID 156 METABOLISM (CAM)

5.1 Introduction and Review 157

5.2 The ecology of CAM in the epiphytes Dendrobium speeiosum 164 Sm. and PZeetorrhiza tridtantata (Lindl.) Dockrill, (Orchi daceae)

5.2.1 Introduction 164

5.2.2 Selection of site, species and individuals 164

5.2.3 Methods 168 - leaf acidity - diffusive resistance of leaf - leaf surface temperature - air temperature - solar radiation - relative humidity - vapour pressure deficit

5.2.4 Re~ults 170

5.2.5 Discussion 179

5.2.6 Conclusions 183 Research needs into CAM in these species 183

5.3 Discussion on CAM in the Australian vascular epiphyte 185 flora

GENERAL CONCLUSIONS 193

Bibliography 197

Appendix 1 - descriptive illustrated key to the Australian vascular epiphyte flora - separate volume

Appendix 2 210

Appendix 3 225 ------·-·------··------·-----·- ·------·--·------·· ~----·-----·------~--· ------,-. '"''"- ___ ..:... .. --::;_., ______··.:·=--==--=-~

vii

List of Tables Page 2.la Australian vascular cpiphyte flora list 27 2.lb Geographic distribution patterns 49 2.lc Life form groupings 50 2.ld Physiognomic types etc 50 2.le Exposure preference index means of groups 50 2.lf CAM in the Australian vascular epiphytes 50 2.lg Disseminule type groupings 50 2.2 Floristic diversity of epiphyte distributional areas 59 2.3 Southward decrease in epiphyte diversity 61

3.1 Climatic parameters of the subtropical sites 93

4.2.3.la Phorophytes of Darrigo STRf 106 lb Epiphytes II II II 107 2a Phorophytes of Shelly Beach LRf 110 2b Epiphytes II II II II 111 3a Phorophytes of Long Point DRf 113 3b Epiphytes " II II " 114 4a Phorophytes of Humber Hill WTRf 116 4b Epiphytes ., II II II 116 Sa Phorophytes of Wrights Lkt CTRf 119 Sb Epiphytes " II II II 119 6a Phorophytes of Leo Ck SEVF 121 6b Epiphytes " II II II 122 4.7 Summary of phorophyte & epiphyte parameters of the plots 125 4.8 Comparative abundance of physiognomic types and life forms 131 4.9 Specificity of common epiphytes in recording plots 134

4.10 Prolific & axenic phorophytes of the recording plots 137

5.1 Data from Long Pt. CAM studies, winter 221 5.2 " II II " II II spring 222 5.3 II II II " II " summer 223 5.4 II II II " " " autumn 224 viii

4.2.6 Trunk/branch transects on Aaronyahia & Endiand:r>a, Leo Ck. SEVF 124 4.2.7 Epiphyte distribution chart, SZoanea, Darrigo STRf 108 4. 2.8 II II II Tristania, Shelly Bch LRf 111 4.2.9 II " II PZanahoneZZa, Long Pt DRf 114 4.2.10 II " II SahizomeY'ia, Humber Hill WTRf 117 4.2.11 II II II Rhodhamnia, Leo Ck SEVF 123 4.2.12 II II II CT'yptocarya, 11 .. " 123 4.3.1 Nest-epiphyte communities 153

5.2.1 (Graph) CAM ecology & physiol., D. speciosum, tree sun, 211,212 winter 5.2.2 II II II II II II II tree shade, 211,212 winter 5.2.3 II II II II II II II rock, winter 213,214 5.2.4 II II II II II PZectorrhiza II 213,214 5.2.5 II II II II II D. speciosum, tree sun, 215,216 spring 5.2.6 II II II II II II II tree shade, 215,216 spring 5.2.7 II II II II II 11 11 rock, spring 217,218 5.2.8 II II II II II PZectorrhiza 11 217,218 5.2.9 II II II II II D. speaiosum, tree sun, 219,220 summer 5.2.10 ... II II II II II II tree shade, 219,220 summer 5.2.11 II II II II II II II rock, summer 171,172 5.2.12 II II II II II PZectorrhiza II 171,172 5.2.13 II II II II II D. speciosum, tree sun, 173,174 auttmin 5.2.14 II II II II II II II tree shade 173,174 autumn 5.2.15 II II II II II 11 11 rock, autumn 175,176 5.2.16 II II II II II PZectorrhiza autumn 175,176 5.2.17a,b Thermohygrographs, winter, Long Point 221 5.2.18a,b II spring, II II 222 5.2.19a,b II summer, II II 223 5.2.20a,b II autumn, 11 11 224 5.3.1 Epiphytes on Ficus, Darrigo STRf in relation to CAM 188

6.1 Mineral analyses from D. speciosum & PZectorrhiza 225 ix

List of Figures Page 3.la Continental distribution of rainforest and MAR 73 3.lb Average annual potential evaporation 73 3.2a Dorrigo STRf macrovegetation profile 74 3. 2b Shelly Beach LRf 11 11 74 3.2c Long Point DRf II II 74 3.2d Humber Hill WTRf II II 75 3.2e Wrights Lookout CTRf 11 II 75 3,4 Air movement at 2 levels in Dorrigo STRf and Long Pt DRf 75 3.5a Light intensity at 2 levels in Dorrigo STRf 76 3.6a Temperature maxima and minima 11 II II 78 3. 7a(i) Summer thermohygrographs II II II 78 3.7a(ii) Winter II II " " 78 3.5b Light intensity in Shelly Beach LRf 79 3.6b Max./min. temps II II II II 81

,, II 3. 7b ( i) Stumner thermohygrographs 11 81 3. 7b ( ii) Winter II ti II II 81 3.5c Light intensity in Long Point DRf 82 3.6c Max./min. temps II II II II 83 3. 7c(i) Summer thermohygrographs" 11 II 83

11 11 11 3. 7c(ii) Winter 11 83 3.5d Light intensity in Humber Hill WTRf 84 3.6d Max./min. temps. II II II 86 3. 7d(i) Summer thermohygrographs 11 11 II 86 3. 7d ( ii) Winter 11 11 11 11 86 3,5e Light intensity in Wrights Lookout CTRf 87 3 .6e Max./min. temps 11 11 II II 88 3.7e(i) Summer thermohygrographs 11 , II II 88 3 • 7e ( ii) Winter 11 11 II II 88

4.1 (Graph) Epiphyte concentration per dbh on Dendrocnide 142 4.2 11 11 11 11 11 11 Cryptocarya 142 4.3 II II II II II 11 Backhousia 143 4.2.1 Trunk/branch transect, Ficus watkinsiana, Dorrigo STRf 109

11 11 4.2~2 " Tristania/Ficus, Shelly Bch. LRf 112

11 11 4.2.3 " Backhousia sciadophora, Long Pt DRf 115 4.2.4 II II II Schizomeria ovata, Humber Hill WTRf 118 4.2.5 II II II Nothofagus, Dicksonia, Wrigts Lkt 120 CTRf X

List of Plates Page

2.1 falcatus 63 2.2 Sarcochilus ceciliae 63 2.3 Sarcochilus tricalliatus 64 2.4 II fl 64 2.5 Sarcochilus serrulatus 65 2.6 Sarcochilus australis 65 2.7 Myrmecophilous epiphyte community 67 2.8 fl II II 67 2.9 Platycerium veitchii 54 2.10 tetraphylla 2.11 Ficus watkinsiana 56 2.12 Bulbophyllum nrinutissimum 56

3.1 View over canopy, STRf, Derrigo NP 77 3.2 Sub-canopy view II II fl 77 3.3 Canopy of LRf, Shelly Beach 80 3.4 Sub-canopy view, LRf 80 3.5 Sub-canopy'view, WTRf, Humber Hill 85 3.6 CTRf, Wrights Lookout 85

4.1 Upper shade-epiphyte community 149 4.2 Shade conununity of semi-epiphytic climbers 149 4.3 Asplenium australasicum nest-epiphyte community 150 4.4 II II II II II 150

5.2.1 Dry Rainforest margin, Long Point 165 5.2.2 Dendrobium speciosum, tree 165 5.2.3 Dendrobium speciosum, rock plant 166 5.2.4 D. speciosum leaf with sunburn 166 5.2.5 PZectorrhiza tridentata 167 5.2.6 P. tridentata microhabitat 167 xi

List of Abbreviations Afr. NT Northern Territory Amer. America NVF complex notophyll vine forest (STRf) Austr. Australia NZ New Zealand C. Cape NSW New South Wales ca. about oc·cas. occasionalCly) Pac Pacific CAM Crassulacean Acid PAR Photosynthetically Active Radiatn. Metabolism Pen. Peninsula cm centimetre(s) Qld Queensland cosmopol. cosmopolitan R. River CTR£ cool temperate Ra Range rainforest (MFF*) rft rainforest diam. diameter SEC Semi-epiphytic climber SEVF* semi-evergreen mesophyll vine DRf dry rainforest forest (tall monsoon rft) (MV'i'* or SEVT*) SEVT* semi-evergreen vine thicket DVT* deciduous vine thicket (Bottle Tree scrub to relict E east rft scrub or DRf) Ect rft/open community SNEVF* simple notophyll evergreen (ecotone) vine forest (WTRf) esp. especially s south Fig. Figure sp. species (singular) Fl. flowering (period) spp. species (plural) fls. flowers ssp. subspecies incl. including infl. inflorescence STRf subtropical rainforest (NVF*) Is. Islands Tas. Tasmania lvs. leaves tblds tablelands LRF littoral sul::tropical rainforest (NVF*) temp. temperature m metres trap. tropical MAR Mean Annual Rainfall usu. usually MFF* microphyll fern forest var. variety (CTRf) Vic. Victoria mm millimetres w west Mt. Mount, Mountain Wdl woodland MVF* mesophyll vine forest (trap. rft) WSF wet sclerophyll forest or tall open forest MVT microphyll vine thicket WTRf warm temperate rainforest (DRf) (SNEVT*) MVW* microphyll vine woodland (rft relict scrub) ± more or less

N north µE, µEin microeinstein, unit of irrad­ N. Cal. New Caledonia iance (quantum) NG New Guinea

* Following Webb, 1978 -----.--.-----,------.-.---, ~ .. ~- .. -·-~------.. ~_.------

xii Abstract

Firstly, recent literature dealing with the systematics and ecology of vascular epiphytes is reviewed, as are a selection of older key papers. The classification and terminology of vascular epiphytes is briefly reviewed and discussed and the system used here is delineated; tenns are defined, including a ntnnber of new and previously ill-defined ones.

The Australian vascular epiphyte flora is then described in a tabulated list and in a more detailed, illustrated descriptive key (Appendix 1). The flora is next discussed in relation to its taxonomic composition, diversity and affinities biogeography, life forms and physiognomic forms, and diaspore dispersal methods; these are also briefly related to basic ecology of the groups.

Next, physical ecological factors of epiphyte environments in Australia are investigated. This includes discussion of continental macroclimate and its bearing on the distribution of epiphyte-favoured vegetation types, particularly rainforests, and investigation of microclimate components at different levels within selected sites in five different rainforest subformations of the subtropics. The results of this show that microsites near the canopy are considerably brighter, drier and more temperature-extreme than are those near the tree trunk bases.

Beginning with a review of relevant works, the synecology of epiphytes is next discussed and the system of study for use here is outlined. The epiphytic vegetation of five subtropical sites (those mentioned above) and a tropical one, are investigated using this system which involves marked plots and the recording of all trees and epiphytes within them. The data derived from these are used in conjunction with that mentioned above and other observations for comparison and discussion of such topics as epiphyte floristic diversity, population density, vegetational complexity, occurrence of different epiphyte forms, specificity of epiphyte/phorophyte relationships, phorophyte axeny and epiphyte-proneness, allelopathy and phorophyte age ef~ect. Observations and review on nest-epiphytes and succession are discussed.

Some basic functions of CAM in two epiphytic orchids were investigated under field conditions and the results are discussed in relation to its adaptive significance; the results of a survey of CAM in the Australian epiphytes are discussed and from this and the former, it is concluded that CAM is a very important water-conserving mechanism particularly to the heliophilous epiphytes. Relevant literature is reviewed.

It is generally concluded from all of the above that epiphytism has been developed by small, slow-growing to avoid competition for light and in doing so, they have had to concomitantly adapt to water-stress and nutrient deficiency. 1

General Introduction

According to the Oxford English Dictionary, the word epiphyte, in botanical 1 usage , means a plant whiah grows on another plant; usually restricted to those which derive only support (not nutrition) from the plants on which they grow. From the same authority, it was first used in the literature by John Lindley in 1830 (in Nat. Syst. Bot. 264, as the derived adjective epiphytic). Its etymological origin is from the Greek epi, upon+ phyton, plant (Flood, 1960). Thus, other reference texts give the meaning of epiphyte as, e.g., a plant which grows on other plants but not parasitically; - an air plant (Jackson, 1928); a plant growing on another plant but not deriving food from it (Usher, 1966); plant attached to another plant, not growing parasiticaUy upon it but merely using it for support (Abercrombie et al. , 1966) ; ••• and so on.

From these the meaning appears to be clea.r but still certain ambiguities r~main. For instance, most definitions refer to the epiphyte not deriving nutrients from its substrate plant but many studies show that some, even most of the minerals absorbed by many epiphytes, come from stemflow much of which mineral content is leached from the phorophyte (bearer-plant). Most writers have interpreted the word to mean non-parasitic i.e., such nutrient sources used by the epiphyte are not available to the phorophyte (but see, however, Herbert, 1958, and Nadkarni, 1981, reviewed in Ch. 1). Even so, epiphyte is sometimes used in a broad sense to include parasites such as mistletoes.

Another problem, less easily disposed of, centres on the growing upon part of the definition. Lianas growing upon trees could perhaps, in the broadest sense, be called epiphytes but these are usually classified separately as most do not attach themselves to their support by actually growing onto it. There are some however, that do attach by growing adventitious roots onto the support and sometimes these roots may ramify and produce substantial root systems. As such, they probably derive nutrients from the outer, dead tissues of the support plant and from stemflow

1. N. B • the same word is used in pathology in reference to a plant, e.g. fungus, growing on the skin of an animal. 2

etc. Such vine /epiphytes are a problem as the classical definition does not exclude plants that grow upon a bearer-plant as 1.veU as in the soil at 1 the same time . A further clarification of the definition, involving major source of nutrients would appear to be useful (see Ch. 1.2).

Epiphytes have fascinated botanists ever since Europeans first ventured to the tropics where vascular epiphytes are common, varied and prominent in many different plant communities. Columbus is credited with the first recorded comment on vascular epiphytes when he wrote in his log in 1492 that many of the tropical trees "have a great variety of branches and leaves, all of them growing from a single root" (from Gessner, 1956). Perhaps most of the plants transported from the tropics to Europe for the horticultural trade from the 17th century to the present, have been epiphytic species of orchids, bromeliads, aroids, ferns and others. Not only are they attractive, with highly ornainental foliage, inflorescences and flowers but they are a small and manageable size at maturity. Also they are often± strongly drought tolerant with minimal nutrient needs and thus may thrive on neglect, an important necessity of indoor plants for people who appreciate their beauty without appreciating cultural requirements, or are forgetful or neglectful.

Probably the most intriguing attribute of epiphytes is that they grow independent of the ground and that this is their normal, 'chosen' way of life. From this arise the questions of how they manage to survive and indeed, thrive in such apparently arid and nutrient-poor situations, especially since other plants have their roots in the ground where they are protected and water and minerals are not severely limited. Also the environmental forces that gave rise to·the development of the epiphytic way of life, the mode of development and evolutiona~y steps and the phyletic origins of epiphytes all pose questions of great interest. Though basically of a survey/review type, this dissertation attemps to clarify some of these problems.

More specifically, the Australian vascular epiphytes have not been the subject of a comprehensive study previously and the present one is an attempt at laying some groundwork and initiating some specific lines of

1. A separate group, viz, semi-epiphytic climbers, has been instituted here to accommodate these (see Ch. 1.2). 3

investigation. Accordingly, the epiphytic flora has received considerable attention in this report and more specific reasons for this are detailed in the introduction to the flora chapter (Ch. 2).

Similarly, the synecology of the epiphytes has been little studied and this has been approached here by developing a system of recording of data from plots in different rainforests as a basis for comparison and discussion. Five such epiphyte recording plots were in the subtropics but only one tropical representative was investigated, owing partly to the great distances involved and the associated expense and partly also to the writer's experience with the tropical disease Leptospirosis while there.

Defining and characterising epiphyte microhabitats present great problems relating to the number of ecological variables, their fluctuation over even very short distances, and their interactions with one another. The patchiness of substrate and the importance of the vertical dimension in epiphyte ecology multiply these problems. Even so, some attempt is made in this study to coarsely characterise macro-microhabitat physical factors to relate to the flora and vegetation work. A full attempt at such an investigation will require a major project with the emphasis on this aspect and will involve considerable equipment (and expense), extensive data collection and appropriate analyses.

The ecology and adaptive significance of the physiological mechanism known as Crassulacean Acid Metabolism (CAM) has been investigated in two epiphytic orchids under natural field conditions and a survey of CAM in the Australian epiphytes was carried out in co-operation with others in an attempt•to assess its importance in the ecology of epiphytes.

For several reasons, non vascular epiphytes are not investigated in this study. The state of and naming of the Australian flora requires a great deal more work to bring it to a state where it can be readily worked with by non-experts in that field. Also, their physiology, especially water relations and poikilohydry set them clearly apart from most vascular epiphytes and give rise to ecological relations that are also quite different. For these reasons particularly, they require specialisation of study.

Thus, N.B. in the present work, where the word epiphyte is used without qualification, it is to be taken as referring to vascular epiphytes.