582.772.2:581.145.1 MEDEDELINGEN LANDBOUWHOGESCHOOL WAGENINGEN • NEDERLAND • 76-2 (1976) FLOWERING AND SEX EXPRESSION IN ACER L. A BIOSYSTEMATIC STUDY (with a summary in Dutch) P. C. DE JONG Department of Plant Taxonomy and Plant Geography, Agricultural University, Wageningen, The Netherlands (Received4-XI-1975 ) Date of publication • 7 April 1976 H. VEENMAN &ZONE N B.V.- WAGENINGEN - 1976 ?i>^ c ABSTRACT JONG, P. C. DE (1976). Flowering and sex expression in Acer L. A biosystem- atic study. Meded. Landbouwhogeschool Wageningen 76-2, 201 pages, 34 figures, 24 tables, 229 references, Dutch summary. A review and an analysis is given of flowering and sex expression in Acer. The process of sex differentiation was studied in physiological experiments and could be influenced by accelerated flowering and by removal of $ flower buds just after bud break. The paper further includes notes on the morphology, mainly of the reproductive organs, and a study of floral morphogenesis. A taxonomie study led to the division of Acer into 15 sections, partly subdivided into 2-3 series. Of these series, two, Ukurunduensiaan d Wardiana,ar e described for the first time. A key to the sections and series is added. The evolution of Acer, especially of its flowering and sex expression, and of its morphological characters, isdiscussed . Notes on sex expression in related genera are included. Descriptors: morphology, floral morphogenesis, sex differentiation, taxo­ nomy, evolution, Dipteronia, Aesculus, Koelreuteria. Mededelingen Landbouwhogeschool Wageningen 76-2 (1976) (Communications Agricultural University) is also published as a thesis CONTENTS 1. GENERAL INTRODUCTION 1 1.1. The genus Acer 1 1.2. Flowering and sex expression 3 1.3. Scope of investigations 4 2. MORPHOLOGY 5 2.1. Introduction 5 2.2. The flowers 5 2.2.1. The number of floral parts 5 2.2.2. The occurrence of a connate perianth 7 2.2.3. Distinction of calyx and corolla 8 2.2.4. The arrangement of the stamens 8 2.2.5. The honey disc 10 2.2.6. The style and stigmas 10 2.2.7. The pollen 11 2.3. The inflorescence 12 2.3.1. Classification 12 2.3.2. Terminal and lateral inflorescences 14 2.3.3. The abscission of blown (male) flowers 15 2.4. The sexuality in Acer 16 2.4.1. The sexuality of the flowers 16 2.4.2. The sex expression of inflorescences 17 2.4.3. The sex expression of plants 17 2.4.4. The sex expression of species 18 2.5. The fruit 19 2.5.1. The shape of the fruit 19 2.5.2. The parthenocarpic fruit 19 2.6. The seed 21 2.6.1. The embryo 21 2.6.2. Two-seeded mericarps 22 2.6.3. Seed germination 22 2.7. The bud scales 22 2.8. The leaves 23 3. FLOWERING AND SEX EXPRESSION (OBSERVATIONS) 25 3.1. Introduction and literature 25 3.2. Materials and methods 28 3.3. Results of observations per section 30 I. Section Acer 30 A. Series Acer 30 1. Introduction and literature 30 2. General observations on flowering 33 3. Variation inflowering type s 33 4. Studies on a road side planting near Boskoop 35 5. Stability of protogynous flowering 37 6. Annual variations in trees with a <Jiphas e 37 7. Variations in the number of $flowers pe r inflorescence 38 8. Occurrence of a second $ phase 40 9. Variation in the sex expression of the terminal flowers 40 10. Clonal varieties and rootstocks 42 11. Flowering on one-year-old long shoots 42 12. A very heterogeneous flowering tree 43 13. Absence of a $ phase 43 14. Degree of variability within the series 43 B. Series Monspessulana 44 C. Series Saccharodendron ' 44 1. Introduction and literature 44 2. Results of observations 45 3. Degree of variability within the series 45 II Section Platanoidea 45 A. SeriesPlatanoidea 45 1. Introduction and literature 45 2. General observations on flowering 47 3. Variation inflowering type s 50 4. Relations between flowering type, flowering time and number of flowers per inflorescence 50 5. Flowering on one-year-old long shoots 51 6. Clonal varieties and rootstocks 53 7. Stability of protogynous flowering 53 8. Absence of a $ phase 53 9. Failure of sex expression on the borderline of the ? and o*nphase s ... 55 10. An apparently S tree 55 11. Occurrence of a second $ phase 55 12. Degree of variability within the series 55 B. Series Pubescentia 56 III Section Palmata 56 1. Introduction and literature 56 2. General observations on flowering 56 3. Variations inflowering type s 58 4. Clonal varieties and rootstocks 58 5. Stability of protogynous flowering 58 6. Two male A.palmatum cv. 's 58 7. Variability in A. circinatum 58 8. Degree of variability within the section 61 IV Section Macrantha 61 A. Series Tegmentosa 61 1. Introduction and literature 61 2. General observations on flowering 63 3. Annual variation in the sex expression 63 4. The variation in sex expression within a single specimen 67 5. Occurrence of bisexual flowers 71 6. Degree of monoecious flowering within the series 71 B. Series Wardiana 72 V Section Parviflora 72 A. Series Parviflora 72 B. Series Ukurunduensia 72 C. Series Distyla 74 VI Section Trifoliata 74 1. Introduction and literature 74 2. General observations on flowering 75 3. Annual variation in flowering 75 4. Degree of variability within the section 77 VII Section Rubra 78 1. Introduction and literature 78 2. General observations on flowering 82 3. Annual variation in the sex expression 84 4. Occurrence of bisexual flowers 84 5. Relation between the number of stamens and the sex expression of the flowers of A. saccharinum 85 6. Degree of variability within the section 86 VIII Section Ginnala 86 1. Introduction and literature 86 2. Results of observations 86 3. Occurrence of a second ? phase 88 IX Section Lithocarpa 88 A. SeriesLithocarpa 88 B. Series Macrophylla 88 1. Introduction 88 2. General observations on flowering 88 3. Occurrence of bisexual flowers 90 X Section Negundo 90 XI Section Glabra 93 A. Series Glabra 93 B. Series Arguta 94 XII Section Integrifolia 94 A. Series Trifida 94 B. Series Pentaphylla 94 XIII Section Indivisa 94 XIV Section Hyptiocarpa 96 3.4. Some notes on monoecism in related taxa 96 3.5. Discussion and conclusions 99 3.5.1. Sex expression of individual plants 99 3.5.2. The effects of variable sex expression within the species 100 3.5.3. Classification of Acer on the basis of the variability in sex expression ... 101 3.5.4. Sex expression versus sex differentiation 103 4. FLORAL INITIATION AND PREFLORAL DEVELOPMENT 104 4.1. Introduction 104 4.2. Initiation of inflorescences 104 4.3. Initiation of flower buds 105 4.4. Initiation of floral organs 105 4.5. Morphogenesis of the stamens 106 4.6. Morphogenesis of ovaries 107 4.7. Discussion and conclusions 108 5. THE PHYSIOLOGY OF SEX DIFFERENTIATION 110 5.1. General introduction 110 5.2. The influence of acceleratedflowering o n the sex expression 110 5.2.1. Introduction and literature 110 5.2.2. Materials and methods 110 5.2.3. Results (per section) Ill 5.3. Influence of defoliation on the sex expression 120 5.3.1. Introduction and literature 120 5.3.2. Defoliation after flower induction 120 5.3.3. Defoliation during unfolding of the leaves 121 5.4. Influence offlower bud s on the sex expression 121 5.4.1. Introduction and literature 121 5.4.2. Materials and methods 121 5.4.3. Results 122 5.5. In vitro culture offlowers an d flower buds 126 5.6. Viability of pollen 126 5.7. General discussion and conclusions 127 5.7.1. Preliminary remarks 127 5.7.2. Differentiation of primary <J flowers 128. 5.7.3. Differentiation (of (primary) $ flowers 131 5.7.4. Differentiation of secondary <J and $ flowers 131 6. TAXONOMY 133 6.1. Historical survey of genus and family 133 6.2. Survey of classifications 134 6.3. Criteria for a new classification 135 6.4. Proposed classification of the genus Acer 136 6.5. Key to the sections and series 155 6.6. Survey of biosystematic studies 157 6.6.1. Anatomy 157 6.6.2. Chemistry 158 6.6.3. Karyology 159 6.6.4. Genetics 159 6.6.5. Heteroplastic grafting 160 6.7. Palaeotaxonomy 160 7. EVOLUTION 162 7.1. Introduction 162 7.2. Literature 162 7.3. Phylogenetic developments of morphologic characters 164 7.3.1. The inflorescences 164 7.3.2. The flowers 165 7.3.2.1. The perianth 165 7.3.2.2. The androecium 165 7.3.2.3. The honey disc 166 7.3.2.4. The pistil 166 7.3.3. The fruits and seeds 166 7.3.4. The leaves 167 7.3.5. Bud scales and shoot development 168 7.4. Evolution offlowering an d sex expression 168 7.5. Contribution of the remaining biosystematic and morphologic studies . 170 7.6. Discussion and conclusions 171 SUMMARY 175 ACKNOWLEDGEMENTS 179 SAMENVATTING 180 REFERENCES 184 SPECIMENS EXAMINED 192 1. GENERAL INTRODUCTION 1.1. THE GENUS ACER The Aceraceae contain two genera: Acer and the small genus Dipteronia. The family belongs in the Sapindales, and is rather closely related to the Sapindaceae and Hippocastanaceae. The maples are trees and shrubs characterized by opposite leaves and a winged schizocarpic fruit, the samara. The leaves show a large variability within the genus. Most common are 3- or 5-lobed leaves, while also unlobed, 7-13-lobed, trifoliolate, palmatifoliolate or pinnate leaves occur (see fig.