Myrtaceae

Variation in Myrtaceae flowers and fruits.

Variation in Myrtaceae flowers and fruits. Photos: E. Lucas, G. Bramley, F. Forest.

Introduction

The Myrtaceae (Eucalyptus, clove or guava family) is an ecologically important family of c. 140 genera and between 3,800 and 5,600 species. Centres of diversity for the family are in the wet tropics, notably South America, Australia and Tropical Asia. Little baseline knowledge exists for the family and that which is available is 150 years out of date for most tropical areas (except Australia). While resolution of the taxonomy of the family at tribal level is progressing, the need for further work within the largest tribe – the fleshy fruited and primarily Neotropical tribe Myrteae, is great. Due to high morphological variation at all taxonomic levels, Myrtaceae has a reputation in the Neotropics as being a ‘difficult’ family to identify even to genus. Taxonomic data is lacking on every front, the lack of taxonomic revisions matched by the lack of correctly named and curated collections in the world’s herbaria. The subtribal classification of Myrteae is unstable, as are generic boundaries within it,  and the number of undescribed species is high because their description is often frustrated by the difficulty in confidently assigning a specimen to genus.  

Neotropical Myrtaceae are particularly species rich in some of South America’s most threatened habitats. The two largest Neotropical genera are Eugenia and Myrcia comprising approximately >550 and 250-500 species respectively with species diversity reaching its peak in the Brazilian Atlantic rainforest and cerrado, habitats that are disappearing rapidly under human pressure. Only 4% of the Atlantic forest remains, with these fragments containing up to 90 species of Myrtaceae per ha., many of which are undescribed. Because of the importance of Myrtaceae and the degree of skill required to identify its species, a complete ecological description of the areas in which it is so diverse depends upon a taxonomic revision of the family. Such a revision must be undertaken as soon as possible as many of these habitats are disappearing at an unprecedented rate. 

Myrtaceae is economically important in the spice, fruit, timber and pharmacology industries with other economic potential beginning to be realised (bioactive compounds, vitamin-rich soft fruits etc.). Eucalyptus is widely cultivated to provide shade and for the timber and pulp industries. Syzygium aromaticum (clove) and Pimenta dioica (allspice) are important in the spice industry. Pimenta racemosa (bay rum), Melaleuca (cajeput) and Eucalyptus provide oils for the perfume industry, while antiseptic oils are extracted from Eucalyptus, Melaleuca alternifolia (tea tree), Callistemon and Leptospermum. Almost all fleshy fruited Myrtaceae are edible; economically important fruits are Psidium guajava (guava) and Syzygium aqueum (rose apple), with many lesser known species locally important for juice, sweets and jams, such as Myrciaria cauliflora (jaboticaba) and Eugenia uniflora (pitanga). 

The main objectives of the Myrtaceae section are: 1) to continue to play a key role in an international team assessing generic limits and arrangements in tribe Myrteae; 2) to continue to develop and lead international multidisciplinary collaboration in Myrciinae systematics, resolving generic complexes within the subtribe and producing an infrageneric framework of the largest genus in the group – Myrcia s.l.; 3) to continue to produce high quality species-level revisions and checklists of Myrciinae genera; 4) to maintain Kew’s world class Myrtaceae collection of herbarium specimens in a systematically up to date manner, easily accessible to Myrtaceae researchers; 5) to develop a GIS-based biogeographical programme for the Myrciinae, for conservation, environmental monitoring and accelerated production of preliminary IUCN ratings; 6) to encourage and initiate further collaborative research projects within the taxonomic foci of the group; and 7) to develop projects on the traditional and novel uses of species of Myrtaceae (subject to funding). These projects will aim to further our understanding of the economic and social uses of these species and thus support their conservation and sustainable use.

Background

Work on Myrtaceae has been intermittent at Kew since the time of Bentham (generic overview), with a tropical Asian focus in the 1970s (A.J. Scott) and a New World focus since the late 1980s. The current multi-disciplinary collaborative programme has been developed over the last fifteen years, and has its foundations in: 1) Kew’s exceptionally type-rich Neotropical collections; 2) strong cross-departmental links between the herbarium and the Micromorphology, Biological Interactions and Molecular Systematics sections in the Jodrell Laboratory; and 3) nomenclatural expertise (essential in a family where the combined effects of biology and history have often resulted in nomenclatural disorder). Kew staff have a broad generic view across Myrtaceae, however the overall focus of the team is in resolving systematic relationships in the predominantly South American tribe Myrteae and promoting its conservation. At a lower taxonomic scale, the focus is on the core genera of subtribe Myrciinae (Myrcia, Marlierea, Calyptranthes and Gomidesia, c. 700 species and >1,000 binomials). The objectives are achieved by producing consistently high quality data within Kew and from collaboration with an established network of global Myrtaceae researchers.  

Kew’s current work on Myrteae and Myrciinae complements that of Landrum (Arizona State University) and collaborators who have approached the tribe with emphasis on Neotropical Myrtinae, and the paleotropical Myrtinae emphasis of Guymer and Snow (Brisbane Botanic Gardens).Other international collaborations include joint publication with Australian (RBG Sydney) and New Zealand (University of Dunedin) researchers who have produced or contributed to the latest family and tribal level molecular phylogenies. Collaboration is also strong between Brazilian botanists researching ecological issues in Myrtaceae (University of Brasília, UFLA), Myrtaceae-specific data repatriation (University of Feira da Santana) and floristic, herbarium based and molecular systematics of Myrciinae and Eugeniinae (Universities of Belo Horizonte, Campinas, Maringá and São Paulo). Networking with RBG Sydney, Arizona State University, the Marie Selby Botanic Gardens and RBG Edinburgh supports Kew-based molecular systematic and wood anatomical research on the Myrciinae and Myrteae. Kew staff contributed Myrtaceae and Melastomataceae accounts to Heywood’s Flowering Plants of the World and continue to contribute to collaborative Flora projects (e.g. Flora of São Paulo, Flora of the Guianas, Flora Neotropica).

After a slow start as a result of staff changes, the work of the Myrtaceae team is now flourishing; Kew’s high quality, multidisciplinary and collaborative research on Myrtaceae is now entering a new phase, based on the firm foundations set down over the years. 

SIGNIFICANT ACCOMPLISHMENTS (2001 - 2005)

KEY ELEMENTS OF FUTURE PLANS (2006 onwards)

RECENT ACHIEVEMENTS (2001 - 2005)

Collections (2001-2005)

The herbarium collections are maintained in a systematically up to date order with newly published genera and revisions implemented regularly. New material is incorporated into the herbarium within three months of its arrival in the section and incorporation backlogs tackled since 2001 have been significantly reduced. Normally, outgoing loans are processed within six weeks of receipt of request while returning loans are incorporated within eight weeks of arrival in section.

Available figures for 2004 and 2005 indicate that an average of 3,700 specimens are mounted and curated into the Myrtaceae collection per year. An average 300 identifications per year are provided to external institutions and individuals while an average of 150 specimens per year are sent on loan. The section receives visitors amounting to an average of 90 visitor days per year. 

Approximately 200 targeted collections including material for DNA analysis have been made by Kew staff from the Brazilian states of São Paulo, Minas Gerais, Paraná and Rio de Janeiro, and from French Guiana. As a result, over c.200 new Myrtaceae samples have been added to the Kew DNA bank. 

Baseline Plant Diversity Research (2001-2005)

An international Myrtaceae workshop was hosted at Kew in 2005 to consolidate existing inter-institutional collaboration in Neotropical Myrtaceae systematics this provided a networking opportunity for an international team of Myrtaceae experts to review the World Checklist of the Myrtaceae compiled by Rafäel Govaerts. A work providing reliable taxonomic data for c. 5,600 species, which will be of critical use to the wider Myrtaceae community and which contributes to Kew’s advance towards Target 1 of the Global Strategy for Plant Conservation and which is now available online.

Specimen databases have been developed for subtribe Myrciinae (c. 6,000 records to date) and for the large genus Syzygium s.l. (c. 4,100 records). The Myrciinae database is fully georeferenced with all types digitised and has been merged with data from the New York Botanical Garden. The total number of Myrtaceae records in Kew species databases is now c.12,000. 945 Eucalyptus and Angophora species have been imaged and databased as part of the GBIF funded contribution by Kew to the Australian Virtual Herbarium. 

The Myrtaceae account of Flora of Tropical East Africa was published by Bernard Verdcourt in 2001. The new genus Algrizea was published by Eimear Nic Lughadha, Eve Lucas, Elizabeth Woodgyer and co-workers. The Myrtaceae of Mount Jaya (6 species including IUCN conservation ratings) has been published. Accounts of Tristaniopsis and Syzygium for the Tree Flora of Sabah and Sarawak are complete and have been published along with 46 taxa new to science in a separate paper.

Herbarium visits made to Paris, Brussels and St Petersburg, Rio de Janeiro and other local Brazilian herbaria by Kew staff and associates have provided an estimated 1,000 new determinations in these institutions. The visits also laid foundations of understanding of groups in subtribe Myrciinae and have been an essential preliminary step towards the production of the generic/infrageneric framework on which Flora Neotropica revisions of the genera will be based.

Comparative Plant Biology (2001-2005)

Molecular systematic work in the Myrtaceae at Kew has two interconnected main objectives, 1) to provide a phylogenetic hypothesis for evolutionary relationships between the 47 genera recognised in tribe Myrteae and 2) to provide a robust generic/infrageneric framework for genera of subtribe Myrciinae on which future baseline plant diversity research on the four currently accepted genera can be based.

Between 2001-2005, c. 130 Myrteae species representing 33 genera have been sequenced for four gene regions (ITS, ETS, psbA-trnH, matK). Preliminary results elucidating subtribal relationships were published in 2005. More detailed collaborative work within subtribe Myrciinae has been carried out in collaboration with the University of Campinas (Brazil), resulting in the sequencing of a further c. 20 species for the above gene regions except matK. 

A collaborative programme with the University of São Paulo (Brazil) aiming to resolve generic/infrageneric relationships in subtribe Eugeniinae commenced in 2003. This study has sequenced a further c. 60 Eugenia and Eugeniinae species in 10 genera, for all gene regions except matK. 

In excess of 600 new Myrteae sequences have been produced to date.

Morphological studies in subtribe Myrciinae have been carried out in parallel to molecular research. Since 2004, a survey of macromorphological characters has been gathering data from specimens at the Kew, Paris, Brussels and St Petersburg herbaria for a cladistic analysis and detailed review of characters within subtribe Myrciinae. A reduced character set has also been compiled, with which the phylogenetic estimate of tribe Myrteae is being interpreted. 

Wood antatomical studies have surveyed 52 Myrteae taxa for 12 characters and 18 Chamalaucieae taxa for 40 characters.

Comparative research on the distribution of phenolic compounds and polyhydroxyalkaloids in the Myrtaceae has shown that they vary in their distribution. Most species of tribe Myrteae contained polyhydroxyalkaloids, whereas their distribution within the non-Myrteae taxa was sparse. In fact, within these latter taxa the polyhydroxyalkaloids were only found in genera belonging to the Leptospermum and Chamelaucium alliances (sensu Johnson and Briggs 1984) and the new DNA based phylogenies place these alliances in a sister clade to tribe Myrteae.   To date, only a few of the phenolic compounds present in the 268 species studied have been identified. However, the distribution of isorhamnetin, flavones and flavanones in the genera of Calothamnus and Leptospermum suballiances support DNA-based studies that suggest that these two suballiances are not as closely related as previously thought. The phenolic data also supports the DNA-based phlogeny that divides the Calothamnus suballiance into five clades. 

Sustainable Utilisation of Plant Resources (2001-2005)

Taxonomic expertise at Kew supports the Sustainable Utilisation programme in exploring economic potential across the family. Another collaborative research focus is on the insecticidal properties of this understudied group. The project is British Technology Group funded and includes collaboration with the Institute of Arable Crops Research, Rothamsted.

Conservation and Environmental Monitoring (2001-2005)

IUCN conservation assessments were prepared for a total of eleven taxa, seven of which are now published. 

A core fields compliant Myrciinae specimen database has been developed which to date comprises c. 6,000 new, georeferenced records, with over 600 type specimens imaged and databased. Myrciinae specimen datasets from the New York Botanical Garden and the Research Institute for Development – French Guiana are being merged with the Kew database. The database contains some 12,000 records.

FUTURE PLANS (2006 onwards)

Collections (2006 onwards)

The Myrtaceae and Myrtales collections will be maintained in an organised and taxonomically up to date system corresponding to the World Checklist of Myrtaceae. Collections will be curated and protected while making them accessible to researchers and easy to use. High quality curatorial support will continue to be provided to all visitors to the section.

Kew staff will continue to make and acquire targeted Myrtaceae collections with a particular aim to fill gaps in generic and specific representation of tribe Myrteae and subtribe Myrciinae (Myrtaceae).

Baseline Plant Diversity Research (2006 onwards)

The World Checklist of Myrtaceae will continue to be edited and maintained through collaboration with international Myrtaceae researchers and according to the taxonomically up to date arrangement of the Kew Myrtaceae collection, working towards the point where Myrtaceae taxonomy is sufficiently stable for the checklist to be published in hard copy.

Flora Neotropica accounts will be published for Gomidesia and Myrcia s.l. An existing database of c. 2,500 georeferenced Gomidesia records will be made core field compliant and merged with the Myrciinae specimen database. The database will be maintained up to date with all new acquisitions, determinations and georeferences where appropriate. 

The Myrtaceae treatment for the Flora of the Guianas will be initiated, the coordination of contributing authors will be overseen by Kew staff and treatments of Myrciinae genera will be provided.

The problem of excessive names per species in Myrciinae genera resulting from Otto Berg’s ‘taxonomic inflation’ in the 1850’s will be addressed with support from phylogenetic analyses being carried out at Kew and in collaboration with Marcos Sobral (University of Belo Horizonte).  Extensive new synonymisation will be published in Myrcia s.s. This with contributions by Kew staff will be disseminated as a nomenclatural paper while digital images of types of the names concerned will be provided on the internet as part of an on-line database of South American Myrteae.

The Myrciinae database and scanned images of the types will contribute to an online database of South American Myrteae, to be developed in collaboration with the Arizona State University and others. 

A taxonomic revision of Marlierea from South Eastern Brazil will be published in collaboration with the University of Campinas.

A specimen-based checklist of the Myrtaceae of North Eastern Brazil will be published based on data gathered under the Brazilian Data Repatriation Program.

Comparative Plant Biology (2006 onwards)

The current molecular-based phylogeny of tribe Myrteae will be published and character evolution in the tribe examined. Phylogenies will be dated and subjected to biogeographical analysis using a variety of methodologies including dispersal variance analysis (DIVA). Nodes needing better resolution will be identified and targeted for analysis with further gene regions.  Sampling will be increased where possible to represent all Myrteae genera.

A robust phylogeny of Myrciinae will be generated based on morphological and molecular characters, in collaboration with the University of Campinas. Character evolution in the subtribe will be examined and a new infrageneric classification of the Myrciinae will be produced.  

A generic/infrageneric revision of subtribe Myrciinae will be prepared based on the above data. 

A phylogenetic study of Eugenia and subtribe Eugeniinae based on three genes will be published with the University of São Paulo.

The Anatomy of the dicotyledons Myrtales volume will be published as well as broad wood anatomical character surveys of tribe Chamelaucieae and Myrteae.  

The analytical facilities at Kew will be used to identify more of the flavones and flavanones in the Myrtaceae studied so far. The distribution of these compounds among the different alliances will then be compared. It is planned to publish two comparative phytochemistry papers, one on the identification of the flavonoids in different species, and the second on a comparison between the distribution of phenolic and polyhydroxyalkaloid compounds among the alliances being suggested by the DNA-based phylogeny.

A tribal overview of Myrteae phytochemistry, anatomy, macromorphology and molecular systematics will be compiled and published.

Sustainable Utilisation of Plant Resources (2006 onwards)

Kew Myrtaceae staff will continue to contribute occasional advice on Myrtaceae cultivation and management.  Staff will continue to provide expertise for the Sustainable Utilisation programme.

Conservation and Environmental Monitoring (2006 onwards)

IUCN conservation assessments for Gomidesia and Myrcia s.l. will be prepared and disseminated as Flora Neotropica accounts are published.

GIS-based distribution maps of the Atlantic forest/cerrado Myrciinae will be prepared. The diversity of the subtribe in these areas will be examined and the potential use of the tribe for delimiting areas of endemism in Myrciinae and general biogeography will be assessed. Preliminary conservation assessments will be generated from the Myrciinae database for all species from the Atlantic forest/cerrado biomes.

Projects

Biogeography and Conservation of Myrciinae (Myrtaceae)

Chemistry and Biological Activity of Myrtaceae

Myrciinae (Myrtaceae) Genera for Flora Neotropica and Flora of the Guianas

Phylogeny of Eugenia and Eugeniinae (Myrtaceae)

Phylogeny of Subtribe Myrciinae (Myrtaceae)

Phylogeny of Tribe Myrteae (Myrtaceae)

South American Myrteae (Myrtaceae) Online

Systematics and conservation of Western Australian Eucalypts

Tree Flora of Sabah and Sarawak: Myrtaceae

Wood Anatomy of Myrtaceae

World Myrtaceae Checklist and Bibliography

People

Directorate

Neil Brummitt, Stephen Hopper, Eimear Nic Lughadha, Rhian Smith

Herbarium

Peter Ashton (Honorary Research Fellow), Rafaël Govaerts, Laura Jennings, Eve Lucas, Fiorella Mazine (Honorary Research Associate), Justin Moat, Bernard Verdcourt, Elizabeth Woodgyer

Jodrell Laboratory

Mark Chase, Peter Gasson, Elaine Porter, Monique Simmonds

Partners

Australia

Royal Botanic Gardens, Sydney

University of Western Australia

Brazil

Botanical Garden Rio de Janeiro, State of Rio de Janeiro

University of Belo Horizonte, State of Minas Gerais

Univeristy of Brasilia, State of Distrito Federal

Universtiy of Campinas, State of São Paulo

University of Feira da Santana, State of Bahia

University of Maringá, State of Paraná

University of São Paulo, Piracicaba, State of São Paulo

French Guiana

Cayenne Herbarium

Malaysia

Forest Research Institute Malaysia

New Zealand

University of Otago, Dunedin

UK

Department of Plant Sciences, Oxford University

Royal Botanic Garden Edinburgh

USA

Arizona State University

Arnold Arboretum of Harvard University

Missouri Botanical Gardens

New York Botanic Gardens

Selby Botanical Gardens

Publications

Beentje*, H.J. & Smith*, S.A.L. (eds) (2001). Flora of Tropical East Africa, Myrtaceae. Rotterdam: Balkema. 89 pp.

Jansen*, S., Watanabe, T. & Smets, E. (2002). Aluminium accumulation in leaves of 127 species in Melastomataceae, with comments on the order Myrtales. Annals of Botany 90 (1): 53-64.

Khambay, B.P.S., Beddie, D.G., Hooper, A.M. & Simmonds*, M.S.J. (2003). Isolation, characterisation and synthesis of an insecticidal tetramethyltetrahydrochromenedione-spiro-bicyclo{3.1.1}cycloheptane from two species of Myrtaceae. Tetrahedron 59: 7131-7133.

Lucas*, E. (2003). Distribution of Myrtaceae in the Guianas; present knowledge and directions for future studies. Flora of the Guianas Newsletter 14: 93-100.

Lucas*, E.J., Belsham, S.R., Nic Lughadha*, E.M., Orlovich, D.A., Sakuragui, C.M., Chase*, M.W. & Wilson, P.G. (2005). Phylogenetic patterns in the fleshy-fruited Myrtaceae - preliminary molecular evidence. Plant Systematics and Evolution 251: 35-51.

Porter*, E.A. (2004). Distribution of polyhydroxyalkaloids, phenolic acids and flavonoids in the Myrtaceae. PhD Thesis. London: Birkbeck College, University of London. 233 pp.

Sarker, S.D., Bartholomew, B., Nash, R.J. & Simmonds*, M.S.J. (2001). Sideroxylin and 8-demethylsideroxylin from Eucalyptus saligna (Myrtaceae). Biochemical Systematics and Ecology 29: 759-762.

Verdcourt*, B. (2001). Flora of Tropical East Africa, Myrtaceae. Rotterdam: Balkema. 89 pp.

Verdcourt*, B., Eilu, G. & Katende, A. (2002). (1535) Proposal to conserve the name Eugenia bukobensis Engl. (Myrtaceae) with a conserved type. Taxon 51 (2): 389.

Annex material