Distribution information is recorded following the standard of Biological Recording Unit (BRU) (Hollis & Brummitt, 1992), endorsed as an international data standard by the Taxonomic Database Working Group. This standard provides a four-tier hierarchical scheme, with larger countries and larger islands subdivided into geopolitical areas. The 238 countries currently recognised by ISO (ISO, 1993) are divided into 1004 BRUs (see table below).

BRUs (Biological Recording Units) ¹

Level 1 Areas	Level 4 Areas
Europe	58 areas in 45 countries2, of which 7 are subdivided: Greece (2), Italy (3), Spain (2), Russia (6), Ukraine (2) , France (3) and the United Kingdom (3); the remaining countries each equals one level 4 BRU
Africa	76 areas in 60 countries, of which 11 are subdivided: Angola (2) Equatorial Guinea (3), Mauritius (2), Namibia (2), Portugal (3), Réunion (2), Seychelles (2), St Helena (2), São Tomé and Principe (2), South Africa (5) and Spain (3); the remaining countries each equal one level 4 BRU
Asia - Temperate	90 level 4 areas in 35countries, of which 6 are subdivided: China (27), Japan (2), , Taiwan (3), Yemen (2) Georgia (3) and Russia (22); the remaining countries each equal one level 4 BRU
Asia - Tropical	70 level 4 areas in 24 countries, of which 4 are subdivided: India (37), Indonesia (8), Malaysia (3), Papua New Guinea (2); the remaining countries each equals one level 4 BRU
Australasia	17 level 4 areas in 2 countries, of which both are subdivided: Australia (12) and New Zealand (5); the remaining countries each equals one level 4 BRU
Pacific	41 level 4 areas in 25 countries, of which 6 are subdivided: Cook Islands (2), French Polynesia (4), Japan (3), Kiribati (3), Solomon Islands (4), US islands (7); the remaining countries each equals one level 4 BRU
Northern America	98 level 4 areas in 5 countries, of which 3 are subdivided: Canada (15), Mexico (30), United States (52); remaining countries each equals one level 4 BRU
Southern America	127 level 4 areas in 47 countries, of which 13 are subdivided: Argentina (23), Brazil (29), Chile (16), Colombia (3), Costa Rica (2), Ecuador (2), Guadaloupe (2), Honduras (2), Mexico (5), Nicaragua (2), Puerto Rico (2), Venezuela (3) and Netherlands Antilles (2); the remaining countries each equals one level 4 BRU
Antarctic	12 level 4 areas in 8 countries, of which 2 are subdivided: Falkland Islands (3), French Southern Territories (3); the remaining countries each equals one level 4 BRU

1	Hollis, S. and Brummitt, R.K. (1992).
2	ISO Standard 3166 is used by Hollis and Brummitt to define political countries. The units in the ISO standard are countries, dependancies and other areas of special interest for purposes of international exchange, without indicating expression of opinion whatever concerning the legal status of any country or territory or of its authorities or concerning the delimination of its frontiers.

Data are recorded at the finest scale possible within the BRU scheme. For example, if data are provided on the threat status of a plant within individual states of Mexico, then this is the scale at which the data are recorded in the database. However, if data are only provided for a particular plant in Mexico as a whole, then the data can only be recorded in the database at the national level. This unavoidably leads to some inconsistencies and data sets that are not directly comparable, but we feel that it is important to present the data with the most detail possible, even if it occasionally results in a lack of total comparability.

Since BRUs are geopolitically based, they do not cross national boundaries. All BRU units are linked to the appropriate ISO country code, allowing country- level queries to be made even though the data are often stored at a lower level. Some modifications have been made at UNEP-WCMC to the BRU scheme to take political changes since the standard was published into account.