Malesian Euphorbiaceae Newsletter 8

 

March 1998

 

Goto on this page:

Analytical Key to the Genera of the Euphorbiaceae

Revised Genera


Analytical Key to the Genera of Thai Euphorbiaceae

 

Peter C. van Welzen

 

Introduction

 

The present identification key is not the first table to identify the genera of Thai Euphorbiaceae with. Airy Shaw already constructed one in 1972. Unfortunately, one needs complete material, with especially staminate flowers and fruits, to be able to find the correct name with his key. The first half of the key presented here roughly follows the structure of Airy Shaw's key. Whenever possible, vegetative characters are used in the questions, but the use of (difficult) generative questions could not be avoided. The present key has become much longer, 154 couplets of questions, compared to roughly 85 in Airy Shaw's key (1972). This is partly caused by the fact that more exceptions are keyed out (e.g., Croton colobocarpus Airy Shaw, which lacks stellate hairs) and because questions are split into ones for flowering material and others for fruiting material. The questions concerning flowers comprise questions on staminate and pistillate flowers, at least, as far as possible. This should enable users to identify single specimens.

The key is based on the taxa treated by Airy Shaw (1972), generic descriptions as found in Backer & Bakhuizen van den Brink f. (1963), Whitmore (1973), and the material present in the Bangkok Forest Herbarium (BKF). The key in Whitmore (1973) has the same structure as the one constructed by Airy Shaw (1972).

The present key is meant to be tested, because I expect that it is still incomplete. Probably not all specimens will key out correctly. Users are, therefore, kindly invited to send me notes on problems encountered while using the key (see address above, or e-mail: peter.vanwelzen@naturalis.nl). These notes will be used to improve the key. A final and completely functional key will be published in the account on the Euphorbiaceae in the Flora of Thailand.

 

Characters

Some characters are difficult to use. One should carefully examine the following characters:

- Leaves opposite or in whorls versus alternate: the majority of the leaves should be opposite or in whorls. Take care with Mallotus section Hancea: these species have opposite leaves, but one leaf is reduced to an (early caducous) bract.

- Glands. Questions about glands or black glandular areas concern glands or areas present in the basal part of the leaves, often at or near the apex of the petiole on upper or lower surface. Always check several leaves and use a microscope if one is available, otherwise a handlens is a prerequisite.

- Stellate hairs and glandular scales are usually very small and they sometimes appear very infrequently. Again, check several parts, especially the young parts of the branchlets and the lower surface of the leaves close to the basal part of the midrib. Use a microscope or a handlens.

 

The proper key has been updated and can be viewed as a separete file in these webpages: Key to the genera of the Euphorbiaceae in Thailand.

 

Acknowledgements

The help of Stefan Dressler (Bridelia, Cleistanthus), Hans-Joachim Esser (tribe Hippomaneae), Raoul Haegens (Baccaurea), and Anne Schot (Aporosa) in checking several genera is highly appreciated.

This key was constructed during a sabbatical leave, which was granted by the University of Leiden. The following organisations are kindly thanked for their financial support: the Netherlands Foundation for the Advancement of Tropical Research (WOTRO, travel grant no. WR 84-402), the Society for the Advancement of Research in the Tropics (Treub Foundation), and the University of Leiden.

The neighbours and my brother in law are thanked for providing early morning transport to the BKF herbarium and my wife for picking me up in the afternoon.

 

Literature

Airy Shaw, H.K. 1972. The Euphorbiaceae of Siam. Kew Bull. 26: 191-363.

Backer, C.A. & Bakhuizen van den Brink f., R.C. 1963. Flora of Java 1: 441-505. N.V. P. Noordhoff, Groningen.

Whitmore, T.C. 1973. Euphorbiaceae. In: T.C. Whitmore (Ed.), Tree Flora of Malaya 2: 34-136. Longman, London.

 

Revised genera

 

The following genera have been revised:

Genus

World-wide

Malesia

Distribution

Publication

Antidesma

> 150

70

Old world tropics

Kew Miscellaneous ms.

New genus

2

2

SE Asia, Malesia

Blumea ms.

Bridelia

50

15

Old world tropics

Blumea 41 (1996) 263-331

Cephalomappa  

5

5

Malesia

Reinwardtia ms.

Chaetocarpus

11

1

Pantropical

Rheedea 4 (1994) 93-101

Cheilosa

1

1

W Malesia

Blumea 38 (1993) 161-166

Choriceras

2

1

E Malesia, Australia

Blumea ms.

Clonostylis

1

1

Sumatra 

Blumea ms.

Doryxylon

1

1

Philippines, Lesser Sunda Is.

Blumea ms.

Erismanthus

2

1

SE Asia-W Malesia

Blumea 40 (1995) 379-384

Falconeria

1

1

India-SE Asia, Malaysia

Blumea ms.

Fontainea

9

2

E Malesia, Austr., New Caled.

Blumea ms.

Gymnanthes

> 30

2

Pantropical

Blumea ms.

Homalanthus

25

13

Tropical Asia-Australia

Blumea 42 (1997) 421-466

Homonoia

2

1

India-New Guinea

Blumea ms.

Lasiococca

3

1

W Malesia

Blumea ms.

Manihot

100

2

Introduced Malesia

Rheedea ms.

Margaritaria

14

2

Tropical

ms. Barker

Melanolepis

2

1

SE Asia-Pacific

Blumea ms.

Microstachys  

17

1

Pantropical

Blumea ms.

Moultonianthus

1

1

W Malesia

Blumea 40 (1995) 384-388

Neoscortechinia

6

6

Burma to Solomons

Blumea 39 (1994) 301-318

Petalostigma

5

1

E Malesia, Australia

Blumea ms.

Ricinus

1

1

Worldwide

Blumea ms.

Sapium

21

1

Neotropics, cultivated

Blumea ms.

New genus

6

3

Africa, Malesia

Blumea ms.

Spathiostemon

2

2

Thailand, Malesia

Blumea ms.

Stillingia

30

1

Pantropical

Blumea ms.

Strophioblachia

1

1

SE Asia-W Malesia

Blumea ms.

Sumbaviopsis

1

1

W Malesia 

Blumea ms.

Syndyophyllum

2

2

Malesia

Blumea 40 (1995) 388-394

Triadica

2 or 3

2

E Asia, Malesia

Blumea ms.

Trigonopleura

3

3

W Malesia

Blumea 40 (1995) 363-374

Wetria

2

2

Malesia, NE Australia

Blumea ms.