| Abbreviation | Definition |
|---|---|
| HPIB | Harvard Papers in Botany |
| HS | Hybrid Seeds |
| HVGA | Hudson Valley Garden Association |
| HWA | Hemlock Woolly Adelgid |
| IAA | Indole-3-acetic acid |
| IAB | International Association of Bryologists |
| IBA | Indole-3-butyric acid |
| IBG | Idaho Botanical Garden |
| IBI | Index of Biological Integrity |
| IBIS | Integrated Botanical Information System |
| IBIS | Interactive Biodiversity Information System |
| IBPGR | International Board for Plant Genetic Resources |
| IBS | International Bulb Society |
| ICBSE | International Conference on Botanical Science and Engineering |
| ICCP | International Conifer Conservation Programme |
| ICPN | Index To California Plant Names |
| ICRAF | International Council for Research in Agroforestry |
| ICSS | Iowa Cooperative Soil Survey |
| ICST | Inter-Center Strain Trial |
| ICSZ | International Congress on Soil Zoology and Ecology |