| Id. | Group | Links |
| 219 | Acanthaceae | |
| 357 | Acanthasteridae | |
| 359 | Acarapidae | |
| 303 | Acaridae | |
| 360 | Accipitridae | |
| 362 | Acipenseridae | |
| 363 | Actinidiaceae | |
| 381 | Actiniidae | |
| 6 | Acyclic Carbon Compounds | |
| 14 | Adoxaceae | |
| 365 | Aegithalidae | |
| 366 | Aepyornithidae | |
| 375 | Aeshnidae | |
| 18 | Agaricaceae | |
| 20 | Agavaceae | |
| 247 | Aizoaceae | |
| 285 | Aktinida | |
| 364 | Aktinium | |
| 272 | Alcaligenaceae | |
| 370 | Alcedinidae | |
| 28 | Alliaceae | |
| 371 | Alligatoridae | |
| 32 | Aluminium | |
| 8 | Amaranthaceae | |
| 372 | Amaryllidaceae | |
| 42 | Amphisbaenidae | |
| 43 | Anacardiaceae | |
| 369 | Anatidae | |
| 377 | Anguidae | |
| 50 | Anguillidae | |
| 71 | Annonaceae | |
| 379 | Anseranatidae | |
| 380 | Antedonidae | |
| 56 | Antimonium | |
| 60 | Aphididae | |
| 61 | Apidae | |
| 31 | Apocynaceae | |
| 260 | Apodidae | |
| 11 | Aquae mineralia | |
| 213 | Aquifoliaceae | |
| 40 | Araceae | |
| 63 | Araliaceae | |
| 64 | Araneidae | |
| 19 | Araucariaceae | |
| 384 | Ardeidae | |
| 66 | Arecaceae/ Palmae | |
| 386 | Arenicolidae | |
| 67 | Argentum | |
| 348 | Argon | |
| 68 | Aristolochiaceae | |
| 58 | Arsenicum | |
| 70 | Asclepiadaceae | |
| 72 | Asparagaceae | |
| 166 | Aspidiaceae | |
| 276 | Aspleniaceae | |
| 74 | Astacidae | |
| 7 | Asteraceae/ Compositae | |
| 75 | Asteriidae | |
| 80 | Aurum | |