Yams: Botany, Production and Uses

Yams: Botany, Production and Uses

Yams: Botany, Production and Uses

Anthony Keith Thompson and Ibok Oduro

CABI is a trading name of CAB International

© Anthony Keith Thompson and Ibok Oduro 2021. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners.

A catalogue record for this book is available from the British Library, London, UK.

Library of Congress Cataloging-in-Publication Data

Names: Thompson, Anthony Keith (Agriculture), author. | Oduro, Ibok, author.

Title: Yams : botany, production and uses / Anthony Keith Thompson, Ibok Oduro.

Other titles: Botany, production and uses.

Description: Boston, MA : CAB International, [2021] | Series: Botany, production and uses | Includes bibliographical references and index. | Summary: Dioscorea species, commonly known as yam, are tuberous plants which constitute a major staple food in many parts of Africa, Southeast Asia and the South Pacific. This book covers botany, taxonomy, composition and uses, cultivation, production, diseases and pests, and storage-- Provided by publisher.

Identifiers: LCCN 2021006789 (print) | LCCN 2021006790 (ebook) | ISBN 9781789249279 (hardback) | ISBN 9781789249286 (ebook) | ISBN 9781789249293 (epub)

Subjects: LCSH: Yams.

Classification: LCC SB211.Y3 T48 2021 (print) | LCC SB211.Y3 (ebook) | DDC 635/.23--dc23

LC record available at https://lccn.loc.gov/2021006789

LC ebook record available at https://lccn.loc.gov/2021006790

References to Internet websites (URLs) were accurate at the time of writing.

ISBN-13: 9781789249279 (hardback)

9781789249286 (ePDF)

9781789249293 (ePub)

DOI: 10.1079/ 9781789249279.0000

Commissioning Editor: Rebecca Stubbs

Editorial Assistant: Emma McCann

Production Editor: James Bishop

Typeset by SPi, Pondicherry, India

Printed and bound in the UK by Severn, Gloucester

Contents

About the authors

Acknowledgements

Preface

1Introduction

2Botany

Taxonomy

Molecular Taxonomy

Genomics

Breeding

Physiology

3Composition and Uses

Nutrients

Processing

Functional Properties

Food Uses

Non-food Uses

4Cultivation

Propagation

Field Practices

Environment

Staking

Fertilizers

Harvesting

Transport

Yield

5Storage

Preharvest Factors

Storage Structures

Curing

Sprouting

Irradiation

Temperature

Chemicals

6Diseases and Pests

Field Fungal Diseases

Postharvest Fungal Diseases

Specific Fungal Diseases

Control of Fungal Diseases

Bacterial Diseases

Virus Diseases

Physiological Disorders

Insect Pests

Nematode Pests

7Production

Introduction

Some Yam Producing Countries

Trade in Yams

8Some Dioscorea Species

D. abysmophila

D. abyssinica

D. acanthogene

D. acerifolia

D. acuminata

D. aculeata

D. alata

D. alatipes

D. althaeoides

D. altissima

D. antaly

D. arachidna

D. aspersa

D. bahiensis

D. bako

D. balcanica

D. banzhuana

D. batatas

D. baya

D. belizensis

D. belophylla

D. bemandry

D. bemarivensis

D. benthamii

D. bicolor

D. biformifolia

D. birmanica

D. brevipetiolata

D. buchananii

D. buckleyana

D. bulbifera

D. bulbotricha

D. burkilliana

D. burkillii

D. cachipuertensis

D. calicola

D. caucasica

D. cayenensis

D. chingii

D. chouardii

D. cirrhosa

D. cochleariapiculata

D. collettii

D. composita

D. convolvulacea

D. cotinifolia

D. communis

D. coriacea

D. craibiana

D. cubensis

D. cumingii

D. deltoidea

D. demourae

D. divaricata

D. daunea

D. decipiens

D. depauperata

D. doryphora

D. dregeana

D. dumetorum

D. elephantipes

D. esculenta

D. esquirolii

D. exalata

D. fasciculata

D. fandra

D. filiformis

D. flabellispina

D. fordii

D. floribunda

D. futschauensis

D. galeottiana

D. garrettii

D. glabra

D. gracillima

D. gracilipes

D. hamiltonii

D. hastifolia

D. hemsleyi

D. heteropoda

D. hirtiflora

D. hispida

D. hombuka

D. hurteri

D. hypoglauca

D. inopinata

D. intermedia

D. irodensis

D. japonica

D. kamoonensis

D. kerrii

D. kratica

D. laurifolia

D. laxiflora

D. lehmannii

D. linearicordata

D. maciba

D. madecassa

D. mangenotiana

D. marginata

D. melanophyma

D. membranacea

D. menglaensis

D. meridensis

D. mexicana

D. microbotrya

D. minutiflora

D. monadelpha

D. multiflora

D. nako

D. natalia

D. nipponica

D. nitens

D. nummularia

D. opposita

D. oppositifolia

D. orbiculata

D. oryzetorum

D. orangeana

D. ovinala

D. panthaica

D. paradoxa

D. pentaphylla

D. persimilis

D. petelotii

D. pierrei

D. piperifolia

D. pilosiuscula

D. piscatorum

D. poilanei

D. polygonoides

D. polystachya

D. praehensilis

D. prazeri

D. preussii

D. proteiformis

D. pseudonitens

D. pseudotomentosa

D. pteropoda

D. puber

D. pubera

D. purpurea

D. pyrenaica

D. pyrifolia

D. quartiniana

D. quinqueloba

D. racemosa

D. retusa

D. rockii

D. rotundata

D. sagittata

D. sambiranensis

D. sanpaulensis

D. sansibarensis

D. sativa

D. schimperiana

D. scortechinii

D. semperflorens

D. sensibarensis

D. septemloba

D. seriflora

D. simulans

D. sinoparviflora

D. smilacifolia

D. soso

D. spicata

D. spiculiflora

D. spongiosa

D. stemonoides

D. steriscus

D. subcalva

D. subhastata

D. sylvatica

D. tauriglossum

D. tenuipes

D. tentaculigera

D. togoensis

D. tokoro

D. tomentosa

D. torticaulis

D. transversa

D. trifida

D. trifoliata

D. trilinguis

D. undatiloba

D. variifolia

D. velutipes

D. versicolor

D. villosa

D. wallichii

D. xizangensis

D. yunnanensis

D. zingiberensis

References

Index

About the authors

Anthony Keith Thompson is Visiting Professor at King Mongkut’s Institute of Technology Ladkrabang in Thailand and was formerly Professor of Plant Science, University of Asmara, Eritrea; Professor of Postharvest Technology and head of department, Cranfield University, UK; Principal Scientific Officer, Tropical Products Institute, London; Team Leader for EU funded projects in the Windwards Islands and Jamaica; Postharvest Expert for the UN in Sudan, Yemen and Korea for the Food and Agriculture Organization, Ghana and Sri Lanka for the International Trade Centre and Gambia for the World Bank; Advisor to the British, Jamaican and Colombian governments in postharvest technology of fruit and vegetables; Research Fellow in Crop Science, University of the West Indies, Trinidad; Demonstrator in Biometrics, University of Leeds. He has also carried out almost 100 consultancies for various commercial and government organizations in many countries throughout the world. He has published over 100 scientific papers and reports (including eight on yams) and many scientific textbooks.

Ibok Oduro is a Professor at the Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. She is dedicated to promoting indigenous and underutilized food crops in West Africa and her work aims at converting scientific findings into practical solutions. Her interest is in development of competitive products and students’ empowerment on commercialization of research output leading to the establishment of start-ups or spin-off businesses. She has over 20 years of research, theory, practice and policy knowledge, teaching and entrepreneurial experience in development and product diversification of underutilized crops, perishable crops processing, food compositional studies and traditional foods and systems. Professor Oduro teaches both undergraduate and postgraduate students and has supervised three PhD and five masters theses. She has authored over ten research paper publications on yams and more than 100 other publications published in international journals along with five book chapters. Professor Oduro is the Immediate Past first female Provost of the College of Science and the Kwame Nkrumah University of Science and Technology. She was the coordinator for IITA New and Diverse Food Products developed from the D. alata project; Collaborating Scientist for the IFAD/WECARD/IITA project on Poverty Alleviation and Enhanced Food Availability in West Africa through improved yam technologies; and Collaborating Scientist for the Root and Tuber Improvement Programme concerned with on-farm storage of yam tubers.

Acknowledgements

Thanks are due to the following for advice, critical help and allowing the publication of photographs: Sarinya Kumpila; Professor Dr Vincent Lebot; Professor Dr Graham Seymour; Associate Professor Dr Praphan Pinsirodom; Assistant Professor Dr Chirdsak Thapyai; Assistant Professor Jiraporn Sirison; Associate Professor Dr Ratiporn Haruenkit; Ing. Joseph O. Akowuah; Dr Nana Pepra-Ameyaw; Dr (Mrs) Irene A. Idun; Dr Dewayne Stennett; Dr Roger Bancroft; Dr Marcella Corcoran; Pikunthong Nukthamna; Shamina Maccum; and Life Sciences, Springer, Holland.

Preface

When thinking about writing this book we considered primarily what its function should be and, effectively, the purpose of any scientific textbook. Our conclusions were that it should evaluate the current state of knowledge and how this knowledge affects current practices. This would give indications of why this particular industry of yam production and utilization is where it is now and what has influenced it getting there. This, in turn, would influence where it might go in the future. Therefore, our approach to the yam industry in this book has been to review the appropriate literature and reach a consensus on the findings of scientists carrying out research into all aspects of yams. Also, to look at commercial yam production and marketing and the situation in terms of producer countries, in order to give some indication as to why they are at the point they are. This gives an indication of where they could usefully develop in the future. Dioscorea is such a diverse genus in terms of its morphology and chemistry as well as its geographical origin, domestication and breeding, that there is a need to examine Dioscorea species that currently have little or no commercial or domestic value, but might have value in future or could, in some way, contribute to the future production and utilization of this crop.

A challenge in preparing the book is the number of specific and common names applied to yams. In published papers and books, it is often not clear which yam is being referred to. It is not claimed that this book has solved or even usefully contributed to the debate of taxonomists on this issue, but hopefully it makes the situation a little clearer. An example of this challenge is the species D. oppositifolia and D. opposite. It is clear that most authorities accept that they are the same species, but publications may refer to one or the other and it may be a varietal or cultivar difference or they may have even got the species completely wrong. So, we have largely reviewed the work under the specific name given by the authors of the publication or that used by farmers.

A further challenge in producing this book is the number of publications. S.M. Lawani and M.O. Odubanjo produced a bibliography in 1976 which listed 1,562 publications related to Dioscorea, which was, even then, nowhere near complete. So, producing such a book as this will result in justifiable criticism in terms of relevant research that unfortunately has been omitted, but hopefully this criticism will be minimal and positive.

1

Introduction

In this book the name ‘yam’ is applied only to members of the Dioscorea genus, although many other root and tuber crops are sometimes referred to as yams. The name yam derives from older names, including jugnamis, iniamea, yamme and yame. In French the word ignome derives from the earlier igniame. In Spanish they are called niame and nyame. In Portuguese they are called inhame, derived from ynhame. In Dutch they are called iniame. In Italian they are called gname and ignamo. In German they are called ignamkolle and yamswurtzel. In Arabic they are called ighnam. The Mandé groups in West Africa (Benin, Burkina Faso, Côte d’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Niger, Nigeria, Senegal and Sierra Leone) often use the word ‘niam’ for yam (Cumo, 2013).

The order Dioscoreales Hook. f. contains three families: Dioscoreaceae, Burmanniaceae and Nartheciaceae. The highest diversity of the order is in the tropics of South America, the Caribbean islands, Africa, Madagascar, China and Indochina with Dioscoreaceae and Burmanniaceae occurring mainly in the wet tropics and Nartheciaceae mainly in mountainous habitats. Dioscoreaceae was reported to contain four genera: Dioscorea Plum ex L. (653 species); Stenomeris Planch. (2 species); Tacca J.R. Forst and G. 75 Forst (17 species); and Trichopus Gaertn. (1 or 2 species) (Caddick et al., 2002; Govaerts et al., 2007). Tacca was previously in the family Taccaceae. However, it has also been reported that Dioscoreaceae contains six genera: Dioscorea, Epipetrum, Rajania, Stenomeris, Tacca and Trichopus (Burkill, 1960; Coursey, 1967; The Plant List, 2018) although Bornstein (1989) reported that R. Knuth recognized ten genera in Dioscoreaceae in 1930. Wikiwand (2018) reported that there were 613 accepted species and varieties in Dioscoreaceae and the Encyclopedia of Life (EOL, 2019) listed 626 Dioscorea species.

Dioscorea was named after a Greek physician and naturalist called Pedanios Dioscoride. The history of Dioscorea species has been linked to humans for thousands of years by a slow and gradual process of domestication (Ayensu and Coursey, 1972). The occurrence of Dioscorea species in southern Asia, Africa and South America and their domestication in these areas appears directly linked to indigenous populations. Rubatzky and Yamaguchi (1997) reported that artefacts dated about 50,000 BCE from West Africa indicate that wild yams were being used for food at that time and cultivation of yams appears to have developed independently in West Africa, Tropical America and South East Asia from about 3,000 BCE. Since that time some species have been introduced by man from different areas, for example D. alata was introduced at an uncertain date into West Africa, and D. alata and D. esculenta into Tropical America in or after the 16th century (Coursey, 1967).

It was estimated (FAO Stats, 2019) that the area under yam cultivation in 2017 was about 8 million hectares yielding about 73 million tonnes of tubers. Different species had their origin in different parts of the world, but the majority that are used for food are of tropical origin, mainly in West Africa (Table 1.1). However, yams are important in other regions, for example in parts of India (Table 1.2) and South America. Belachew Garedew et al. (2017) reported that in the Sheko district of Ethiopia, yams were a main staple food and farmers were growing D. abyssinica, D. alata and D. bulbifera, with D. alata preferred because of its taste and high yield. Hahn (1995) reported that only six species were of major economic importance as food plants: D. rotundata, D. alata, D. cayenensis, D. bulbifera, D. dumetorum and D. esculenta.

Table 1.1. Geographic origin of what was referred to as the ten most important cultivated Dioscorea species. Modified from Lebot (2019).

Table 1.2. Wild edible tubers, rhizome, corm, roots and stems consumed by the tribal Valaiyans in India. Mohan and Kalidass (2010).

Tubers of Dioscorea species produce a high value food and the plants are easily grown, mature quickly in the right soil conditions and their tubers can generally be stored after harvest for protracted periods. In addition, some species are economically important due to secondary metabolites present in the tubers, particularly diosgenin, which has a molecular structure similar to steroidal hormones and has been used to synthesize steroids for the production of birth control pills. Most Dioscorea species grow best in rainfall greater than 1,500 mm year-1 and require a minimum 6-month growing season with well distributed rainfall, but do not tolerate poorly drained soils or waterlogging. They are mildly drought tolerant but do not compete well with weeds for soil nutrients. Most species should be staked to improve yield, reduce weed competition and the incidence of diseases. Yams exhibit early shade tolerance during establishment but require full sun for optimum yield.

As well as being a starch staple in many areas, some wild Dioscorea species are famine foods and, as mentioned above, others are sources of drugs both in traditional Chinese and Western medicine, including D. nipponica and D. zingiberensis that are major sources of steroid precursors. Abhyankar and Upadhyay (2011) commented that some ethnic groups in India are dependent on plant extracts for curing various ailments, including D. bulbifera, D. aculeata, D. sativa and D. arachnida. This use has been recently decreasing, perhaps because of the lack of confidence of younger generations in traditional medicine and the increasing availability of modern medicines. D. oppositifolia tubers are used in Chinese medicine and as herbal tonics (Tu, 2002). Dried D. japonica tubers were said to be cut into shavings and used in traditional Chinese medicine and as a tonic (Birkill, 1935). In Korea, Kim et al. (2011a) reported that D. japonica tubers have been used as a medicine known as San Yak and they also reported that D. quinqueloba tubers must be correctly prepared for traditional medicine, otherwise their use may cause life-threatening acute kidney injury. D. villosa tubers were reported to be used in traditional medicine by Native Americans in the USA (Moerman, 1998). In parts of India, Choudhary et al. (2009) reported that D. bulbifera was used as a medicinal plant and Swarnkar and Katewa (2008) reported its use as a contraceptive. In summary, Dioscorea species occur throughout the world and have many uses, as well as being a basic staple food.

2

Botany

Dioscorea species are mostly vines (Fig. 2.1) that scramble and twine over other vegetation. The direction of twining of the stems is species-specific (Prain and Burkill, 1938), for example D. zingiberensis, D. sansibarensis and D. tentaculigera twine to the left and D. glabra, D. transversa and D. polystachya twine to the right. Dioscorea species generally have simple cordate leaves, borne on long narrow stems that vary in shape even on the same plant (Fig. 2.2). Dioscorea species bear racemes of inconspicuous dioecious flowers – that is, the male and female flowers are separate and are usually borne on separate plants, although some species may be monoecious. Ding et al. (2000) reported that D. zingiberensis is the only Chinese species recorded as being monoecious, Hawley (1956) reported that the Brazilian species, D. lagoa-santa was monoecious and Hammel (2000) reported that the Costa Rican species, D. lepida was monoecious. Female flowers are borne in axillary spikes (unbranched, indeterminate inflorescences bearing sessile flowers) and male flowers in panicles (inflorescences with many branches) that are up to about 30 cm long (Fig. 2.3). There are many more male than female flowers. The fruit is a dry dehiscent, trilocular capsule varying in size from about 1 to 3 cm long and longer than wide or equally wide as long, depending on species. The capsules contain winged seeds that are dispersed by wind (Figs 2.4, 2.5) (Coursey, 1967; Ding and Gilbert, 2010).

Fig. 2.1. D. alata (a) and D. esculenta (b) growing in a woodland area in Thailand, at Sarinya’s yam farm in Chachoengsao province, eastern region, 2018.

Fig. 2.2. D. pentaphyla (a, b and c) showing different leaves from the same plant and D. oryzetorum (d), all growing at Sarinya’s yam farm, 2018.

Fig. 2.3. (a) Male inflorescences of diploid accessions of D. alata (first two on the left), tetraploid D. alata (third inflorescence) and inflorescences of D. nummularia cultivars; (b) male inflorescences of D. nummularia; (c) and (d) inflorescences of D. nummularia growing in the Pacific islands. Lebot et al. (2016).

Fig. 2.4. Fruit of D. nummularia growing in the Pacific islands: (a) female inflorescence; (b) female inflorescence with developing capsules; (c) capsules with developing seeds. Lebot et al. (2016).

Fig. 2.5. D. glabra – mature fruit in natural forest in Chaiyaphum province in northeastern Thailand. Reproduced with permission of Dr Chirdsak Thapyai.

Two types of tuber are produced by Dioscorea species, those above ground, commonly called bulbils and sometimes referred to as aerial tubers, and those produced below ground that are normally just referred to as tubers or sometimes rhizomes.

Bulbils are produced in leaf axils by some species (Fig. 2.6) including: D. alata, D. bemarivensis, D. bulbifera, D. filiformis, D. kamoonensis, D. oppositifolia, D. pentaphylla, D. persimilis, D. polystachya, D. prazeri, D. puber, D. pyrenaica, D. sansibarensis, D. schimperiana, D. smilacifolia, D. togoensis and D. transversa. Structurally bulbils are stems and have evolved as a method of reproduction, where they may have advantages over underground tubers since they are less dense and can float in water, which may assist distribution in some cases. The limited number of studies conducted on bulbil germination, all performed under laboratory conditions, suggest that bulbils are not dormant and may germinate shortly after dispersal (Okagami and Tanno, 1991). However, Walck et al. (2010) reported that germination of bulbils of D. polystachya in China generally occurs in spring at the beginning of a favourable environment for growth since they are mostly dormant when dispersed in summer or autumn and dormancy can be overcome with cold stratification during winter.

Fig. 2.6. Bulbils from two Dioscorea species: (a) D. bulbifera bulbil in leaf axil; (b) D. bulbifera bulbil sliced longitudinally, both from a wild race in Siritkit Dam, Uttaradit Province of northern Thailand (reproduced with permission of Dr Chirdsak Thapyai); and (c) D. alata var purpurea from Sarinya’s yam farm in Chachoengsao province in the eastern region of Thailand.

In general, there are two types of underground tubers produced by plants: tuberous roots that are lateral roots, modified and enlarged to function as a storage organ – e.g. cassava – and stem tubers that are stems modified and enlarged to function as a storage organ – e.g. potatoes and yams. Stem tubers develop from swellings of stolons arising from the crown of the plant. Stolons generally grow horizontally in the soil as do tubers, but tubers of some species grow vertically downwards in the soil, including D. acuminata, D. daunea, D. filiformis, D. hamiltonii and D. japonica. Tubers can produce new shoots and roots at points along their length to form new plants. Stolons of Dioscorea species vary in length from less than 5 cm to about 50 cm and form from thickened rhizomes where the top parts of the tuber generally produce shoots and the lower parts generally produce roots, but if the top part is removed shoots can be produced from the lower part (Fig. 2.7). At the end of the growing season the tops of the plants die down and after a period of dormancy the tubers begin to regrow. There may be several tubers produced from each plant or there may be only a single tuber.

Fig. 2.7. Yam for sale at a supermarket in Huddersfield in January 2018.

Rubatzky and Yamaguchi (1997) commented that there were some anomalous features of Dioscorea tubers that make them difficult to categorize. These include the lack of remnants of scale leaves or vestigial nodes on the surface, and the fact that they produce no preformed buds or eyes on, or near, the surface as there are in potato tubers. Their growing point may have no terminal bud and most species exhibit strong geotropic growth. Rubatzky and Yamaguchi also pointed out that there was evidence that the Dioscorea storage organ originates from hypocotyl tissue as the first meristematic activity in tuber formation occurs in that region. In tuber growth, the primary meristem is at the distal end. As growth continues, thin layers of meristematic cells are produced beneath the cortex, which, with continued activity, results in the increase in girth. Some of the parenchyma cells just below the epidermis can become meristematic and produce cork cells protecting the tuber (see also ‘Tuber development’, p. 19). Most tubers have a dark brown skin and usually white flesh, although some have other colours. Yams are perennial but the tops die back and there is a period of dormancy before the plant regrows from the tubers. The appearance of small protuberances under the skin layer is an indication of the end of dormancy. The length of tuber dormancy is endogenously controlled but temperature and soil moisture can affect when they regrow. Postharvest, the physiological age of tubers as well as light, temperature, humidity and partial pressure of the surrounding gases can affect when they will regrow (see section on ‘Sprouting’, p. 70).

Taxonomy

Girma et al. (2016) commented that distinguishing Dioscorea species, based on morphological traits, is extremely difficult and unreliable. The number of species reported in Dioscorea varies with different authors but generally it is commonly claimed that it contains around 650 species (Caddick et al., 2002; Acevedo-Rodríguez and Strong, 2005; Govaerts et al., 2007; Lebot, 2009). A total of 1,600 names have been attributed to Dioscorea, among species, varieties and subspecies, with 77 considered as synonyms (The Plant List, 2013). The genus Dioscorea is divided into five clades (sections) within which the species are grouped:

Enantiophyllum, where the vines twine in a clockwise direction, including D. polystachya, D. rotundata, D. alata, D. cayenensis, D. japonica, D. opposita and D. transversa.

Lasiophyton, where the vines twine anti-clockwise , including D. pentaphylla, D. dumetorum and D. hispida.

Opsophyton, where the vines twine anti-clockwise, including D. bulbifera.

Combilium, where the vines twine anti-clockwise, including D. esculenta.

Macrogynodium (Macroura), where the vines twine anti-clockwise, including D. trifida and D. sansibarensis.

IPGRI/IITA (1997) published descriptors of Dioscorea as an aid to identification. This comprehensive list of Dioscorea species is as follows:

D. abysmophila Maguire & Steyerm.

D. abyssinica Hochst. ex Kunth

D. acanthogene Rusby

D. acerifolia Phil.

D. aculeata L

D. acuminata Baker

D. adenantha Uline

D. aesculifolia R. Knuth

D. aguilarii Standl. & Steyerm.

D. alata L.

D. alatipes Burkill & H. Perrier

D. althaeoides R. Knuth

D. altissima Lamarck

D. amaranthoides C. Presl

D. amazonum Mart. ex Griseb.

D. amoena R. Knuth

D. analalavensis Jum. & H. Perrier

D. ancachsensis R. Knuth

D. andina Phil.

D. andromedusae O. Tellez

D. anomala Griseb.

D. antaly Jum. & H. Perrier

D. antucoana Uline ex R. Knuth

D. arachidna Prain & Burkill

D. araucana Phil.

D. arcuatinervis Hochr.

D. argyrogyna Uline ex R. Knuth

D. arifolia C. Presl

D. aristolochiifolia Poepp.

D. asclepiadea Prain & Burkill

D. aspera Humb. & Bonpl. ex Willd.

D. aspersa Prain & Burkill

D. asperula Pedralli

D. asteriscus Burkill

D. atrescens R. Knuth

D. auriculata Poepp.

D. bahiensis R. Knuth

D. bako Wilkin

D. balcanica Kosanin

D. bancana Prain & Burkill

D. banzhuana S.J. Pei & C.T. Ting

D. bartlettii C.V. Morton

D. basiclavicaulis Rizzini & A. Mattos

D. baya De Wild.

D. beecheyi R. Knuth

D. belophylla (Prain) Voigt ex Haines

D. belizensis Lundell

D. bemandry Jum. & H. Perrier

D. bemarivensis Jum. & H. Perrier

D. benthamii Prain & Burkill

D. berenicea McVaugh

D. bermejensis R. Knuth

D. bernoulliana Prain & Burkill

D. besseriana Kunth

D. beyrichii R. Knuth

D. bicolor Prain & Burkill

D. biformifolia S.J. Pei & C.T. Ting

D. biloba (Phil.) Caddick & Wilkin

D. biplicata R. Knuth

D. birmanica Prain & Burkill

D. birschelii Harms ex R. Knuth

D. blumei Prain & Burkill

D. bolivarensis Steyerm.

D. bonii Prain & Burkill

D. bosseri Haigh & Wilkin

D. brachybotrya Poepp.

D. brachystachya Phil.

D. bradei R. Knuth

D. brandisii Prain & Burkill

D. brevipetiolata Prain & Burkill

D. bridgesii Griseb. ex Kunth

D. brownii Schinz

D. bryoniifolia Poepp.

D. buchananii Benth.

D. buckleyana Wilkin

D. bulbifera L.

D. bulbotricha Hand.-Mazz.

D. burchellii Baker

D. burkilliana J. Miège

D. cachipuertensis Ayala

D. calcicola Prain & Burkill

D. caldasensis R. Knuth

D. calderillensis R. Knuth

D. callacatensis R. Knuth

D. cambodiana Prain & Burkill

D. campanulata Uline ex R. Knuth

D. campestris Griseb.

D. campos-portoi R. Knuth

D. carionis Prain & Burkill

D. carpomaculata O. Téllez & B.G. Schub.

D. castilloniana Hauman

D. catharinensis R. Knuth

D. caucasica Lipsky

D. cayennensis Lamarck

D. ceratandra Uline ex R. Knuth

D. chacoensis R. Knuth

D. chagllaensis R. Knuth

D. chancayensis R. Knuth

D. chaponensis R. Knuth

D. chiapasensis Matuda

D. chimborazensis R. Knuth

D. chingii Prain & Burkill

D. choriandra Uline ex R. Knuth

D. chouardii Gaussen

D. cienegensis R. Knuth

D. cinnamomifolia Hook.

D. cirrhosa Lour.

D. cissophylla Phil.

D. claessensii De Wild.

D. claussenii Uline ex R. Knuth

D. claytonii Ayala

D. cochleariapiculata De Wild.

D. collettii Hook. f.

D. communis (L.) Caddick & Wilkin

D. commutata R. Knuth

D. comorensis R. Knuth

D. composita Hemsl.

D. contracta R. Knuth

D. convolvulacea Cham. & Schltdl.

D. conzattii R. Knuth

D. cordifolia Laness.

D. coreana (Prain & Burkill) R. Knuth

D. coriacea Humb. & Bonpl. ex Willd.

D. coripatenis J.F. Macbr.

D. coronata Hauman

D. cotinifolia Kunth

D. craibiana Prain & Burkill

D. crateriflora R. Knuth

D. crotalariifolia Uline

D. cruzensis R. Knuth

D. cubensis R. Knuth

D. cumingii Prain & Burkill

D. curitybensis R. Knuth

D. cuspidata Humb. & Bonpl. ex Willd.

D. cuyabensis R. Knuth

D. cyanisticta J.D Sm.

D. cymosula Hemsl.

D. cyphocarpa C.B. Rob. ex Knuth

D. daunea Prain & Burkill

D. davidsei O. Tellez

D. demourae Uline ex R. Knuth

D. debilis Uline ex R. Knuth

D. decaryana H. Perrier

D. decipiens Hook. f.

D. decorticans C. Presl

D. deflexa Griseb.

D. delavayi Franch.

D. delicata R. Knuth

D. deltoidea Wall. ex Griseb.

D. dendrotricha Uline

D. densiflora Hemsl.

D. depauperata Prain & Burkill

D. diamantinensis R. Knuth

D. dicranandra Donn. Sm.

D. dielsii R. Knuth

D. dissimulans Prain & Burkill

D. divaricata Blanco

D. diversifolia Griseb.

D. dodecaneura Vell.

D. dregeana (Kunth) T. Durand & Schinz

D. duchassaingii R. Knuth

D. dugesii C.B. Rob.

D. dumetorum (Kunth) Pax

D. dumetosa Uline ex R. Knuth

D. ekmanii R. Knuth

D. elegans Ridl. ex Prain & Burkill

D. elephantipes (L'Hér.) Engler

D. entomophila Hauman

D. epistephioides Taub.

D. escuintlensis Matuda

D. esculenta (Lour.) Burkill

D. esquirolii Prain & Burkill

D. exalata C.T. Ting & M.C. Chang

D. fandra H. Perrier

D. fasciculocongesta (Sosa & B.G. Schub.) O. Téllez

D. fastigiata Gay

D. fendleri R. Knuth

D. ferreyrae Ayala

D. filiformis Blume

D. flabellifolia Prain & Burkill

D. flaccida R. Knuth

D. floribunda M. Martens & Galeotti

D. floridana Bartlett

D. fodinarum Kunth

D. fordii Prain & Burkill

D. formosana R. Knuth

D. fractiflexa R. Knuth

D. fuliginosa R. Knuth

D. furcata Griseb.

D. futschauensis Uline ex R. Knuth

D. galeottiana Kunth

D. galiiflora R. Knuth

D. gallegosi Matuda

D. garrettii Prain & Burkill

D. gaumeri R. Knuth

D. gentryi O. Tellez

D. gillettii Milne-Redh.

D. glabra Roxburgh

D. glandulosa (Griseb.) Klotzsch ex Kunth

D. glomerulata Hauman

D. gomez-pompae O. Tellez

D. gracilicaulis R. Knuth

D. gracilipes Prain & Burkill

D. gracilis Hook. ex Poepp.

D. gracillima Miq.

D. grandiflora Mart. ex Griseb.

D. grandis R. Knuth

D. grata Prain & Burkill

D. gribinguiensis Baudon

D. grisebachii Kunth

D. guerrerensis R. Knuth

D. guianensis R. Knuth

D. haenkeana C. Presl

D. hamiltonii Hook.f.

D. hassleriana Chodat

D. hastata Mill.

D. hastatissima Rusby

D. hastifolia Nees

D. hastiformis R. Knuth

D. haumanii Xifreda

D. havilandii Prain & Burkill

D. hebridensis R. Knuth

D. hemicrypta Burkill

D. hemsleyi Prain & Burkill

D. heptaneura Vell.

D. herbert-smithii Rusby

D. herzogii R. Knuth

D. heteropoda Baker

D. hexagona Baker

D. hieronymi Uline ex R. Knuth

D. hintonii R. Knuth

D. hirtiflora Benth.

D. hispida Dennst.

D. holmioidea Maury

D. hombuka H. Perrier

D. hondurensis R. Knuth

D. howardiana O. Téllez B.G. Schub. & Geeta

D. humifusa Poepp.

D. humilis Bertero ex Colla

D. hunzikeri Xifreda

D. igualamontana Matuda

D. incayensis R. Knuth

D. inopinata Prain & Burkill

D. insignis C.V. Morton & B.G. Schub.

D. intermedia Thwaites

D. ionophylla Uline ex R. Knuth

D. iquitosensis R. Knuth

D. irupanensis R. Knuth

D. itapirensis R. Knuth

D. itatiensis R. Knuth

D. jaliscana S. Watson

D. jamesonii R. Knuth

D. japonica Thunb.

D. javariensis Ayala

D. juxtlahuacensis (O. Téllez & Dávila) Caddick & Wilkin

D. kalkapershadii Prain & Burkill

D. kamoonensis Kunth

D. keduensis Burkill ex Backer

D. kerrii Prain & Burkill

D. killipii R. Knuth

D. kimiae Wilkin

D. kingii R. Knuth

D. kituiensis Wilkin & Muasya

D. kjellbergii R. Knuth

D. knuthiana De Wild.

D. koepperi Standl.

D. koyamae Jayas.

D. kratica Prain & Burkill

D. kuntzei Uline ex Kuntze

D. lacerdaei Griseb.

D. laevis Uline

D. lamprocaula Prain & Burkill

D. lanata Bail

D. larecajensis Uline ex R. Knuth

D. laurifolia Wall. ex Hook. f.

D. lawrancei R. Knuth

D. laxiflora Mart. ex Griseb.

D. lehmannii Uline

D. lepcharum Prain & Burkill

D. lepida C.V. Morton

D. leptobotrys Uline ex R. Knuth

D. liebmannii Uline

D. lijiangensis C.L. Long & H. Li

D. linearicordata Prain & Burkill

D. lisae Dorr & Stergios

D. listeri Prain & Burkill

D. litoralis Phil.

D. loefgrenii R. Knuth

D. loheri Prain & Burkill

D. longicuspis R. Knuth

D. longipes Phil.

D. longirhiza Caddick & Wilkin

D. longituba Uline

D. lundii Uline ex R. Knuth

D. luzonensis Schauer

D. macbrideana R. Knuth

D. maciba Jum. & H. Perrier

D. macrantha Uline ex R. Knuth

D. macrothyrsa Uline

D. macvaughii B.G. Schub.

D. madecassa H. Perrier

D. madiunensis Prain & Burkill

D. maianthemoides Uline ex R. Knuth

D. mamillata Jum. & H. Perrier

D. mandonii Rusby

D. mangenotiana J. Miège

D. mantigueirensis R. Knuth

D. margarethia G.M. Barroso E.F. Guim. & Sucre

D. marginata Griseb.

D. martensis R. Knuth

D. martiana Griseb.

D. martini Prain & Burkill

D. matagalpensis Uline

D. matudae O. Téllez & B.G. Schub.

D. mayottensis Wilkin

D. megacarpa Gleason

D. megalantha Griseb.

D. melanophyma Prain & Burkill

D. melastomatifolia Uline ex Prain

D. membranacea Pierre ex Prain & Burkill

D. menglaensis H. Li

D. meridensis Kunth

D. merrillii Prain & Burkill

D. mesoamericana O. Téllez & Mart.-Rodr.

D. mexicana Scheidw.

D. microbotrya Griseb.

D. microcephala Uline

D. microura R. Knuth

D. mindanaensis R. Knuth

D. minima C.B. Rob. & Seaton

D. minutiflora Engler

D. mitis C.V. Morton

D. mitoensis R. Knuth

D. modesta Phil.

D. mollis Kunth

D. monadelpha (Kunth) Griseb.

D. monandra Hauman

D. morelosana (Uline) Matuda

D. moritziana (Kunth) R. Knuth

D. mosqueirensis R. Knuth

D. moultonii Prain & Burkill

D. moyobambensis R. Knuth

D. mucronata Uline ex R. Knuth

D. multiflora Mart. ex Griseb.

D. multiloba Kunth

D. multinervis Benth.

D. mundii Baker

D. nako H. Perrier

D. namorokensis Wilkin

D. nana Poepp.

D. nanlaensis H. Li

D. natalensis R. Knuth

D. natalia Hammel

D. neblinensis Maguire & Steyerm.

D. nelsonii Uline ex R. Knuth

D. nematodes Uline ex R. Knuth

D. nervata R. Knuth

D. nervosa Phil.

D. nicolasensis R. Knuth

D. nieuwenhuisii Prain & Burkill

D. nipensis R.A. Howard

D. nipponica Makino

D. nitens Prain & Burkill

D. nuda R. Knuth

D. nummularia Lamarck

D. nutans R. Knuth

D. oaxacensis Uline

D. obcuneata Hook.f.

D. oblonga Gleason

D. oblongifolia Rusby

D. obtusifolia Hook. & Arn.

D. olfersiana Klotzsch ex Griseb.

D. oligophylla Phil.

D. omiltemensis O. Tellez

D. opaca R. Knuth

D. opposita Thunb.

D. oppositiflora Griseb.

D. oppositifolia L.

D. orangeana Wilkin

D. orbiculata Hook.f.

D. oreodoxa B.G. Schub.

D. organensis R. Knuth

D. orientalis (J. Thiébaut) Caddick & Wilkin

D. orizabensis Uline

D. orthogoneura Uline ex Hochr.

D. oryzetorum Prain & Burkill

D. ovalifolia R. Knuth

D. ovata Vell.

D. ovinala Baker

D. palawana Prain & Burkill

D. paleata Burkill

D. pallens Schltdl.

D. pallidinervia R. Knuth

D. palmeri R. Knuth

D. panamensis R. Knuth

D. panthaica Prain & Burkill

D. pantojensis R. Knuth

D. paradoxa Prain & Burkill

D. pavonii Uline ex R. Knuth

D. pedicellata Phil.

D. pencana Phil.

D. pendula Poepp. ex Kunth

D. pentaphylla L.

D. peperoides Prain & Burkill

D. perdicum Taub.

D. perenensis R. Knuth

D. perpilosa H. Perrier

D. petelotii Prain & Burkill

D. philippiana Uline ex R. Knuth

D. piauhyensis R. Knuth

D. pierrei Prain & Burkill

D. pilcomayensis Hauman

D. pilgeriana R. Knuth

D. pilosiuscula Bertero ex Spreng.

D. pinedensis R. Knuth

D. piperifolia Humb. & Bonpl. ex Willd.