- immortelle
- imparipinnate
- impatiens
- imperfect fungus
- included
- indehiscent
- indumenta
- indefinite
- indian corn
- indeciduate
- indehiscence
- indumentum
- inferior
- inflorescence
- ink-wood
- inky cap
- interfoliaceous
- interfoliar
- internodal
- internode
- introrse
- involucrate
- involucre
- involucrum
- involute
- involution
- ipecac
- iris
- ironwood
- ipecacuanha
- isomerous
- ivory-nut
- ivy
- ivy vine
- jargonelle
- jessamine
- jonquil
- juniper
- jute
- kava
- kelp
- kermes oak
- kernel
- jack
- jasmin
- jenneting
- jill
- jimson-weed
- kale
- kaoliang
- joint
- jugate
- kail
- kali
- kauri
- kidney bean
- knapweed
- labia
- labium
- laburnum
- knot-grass
- kohlrabi
- kola
- labiate
- lapidodendron
- leaf-blade
- legume
- leguminous
- leonurus
- lauraceous
- leaflet
- leafstalk
- lentil
- leucoplast
- liana
- len lity
- liber
- lime-tree
- lignification
- lignin
- lilac
- lima bean
- limb
- limbate
- lime
- linden
- ling
- little-go
- loco
- loculate
- livid
- loculated
- locust-tree
- loofah
- loosestrife
- loquat
- locular
- loculicidal
- lomentaceous
- lotus