| Common Name | Latin Name |
|---|---|
| Ladies' Eardrops | see Redvine |
| Ladysthumb | Polygonum persicaria |
| Lanceleaf Fogfruit | see Fogfruit |
| Lanceleaf Ragweed | Ambrosia bidentata |
| Large Crabgrass | Digitaria sanguinalis |
| Large Hop Clover | Trifolium campestre |
| Large-bracted Plantain | Plantago aristata |
| Late Boneset | Eupatorium serotinum |
| Late Thoroughwort | see Late Boneset |
| Lateflowering Thoroughwort | see Late Boneset |
| Lawn Burweed | Soliva pterosperma |
| Lemon Balm | see Bee-balm |
| Lindheimer's Panic-grass | Dicanthelium acuminatum subsp. Lindheimeri |
| Little Barley | Hordeum pusillum |
| Livid Amaranth | see Purple Amaranth |
| Livid Pigweed | see Purple Amaranth |
| Lizards Tail | Saururus cernuus |
| Long Smooth-fruited Poppy | see Field Poppy |
| Long-beaked Arrowhead | Sagittaria australis |
| Long-stalked Phyllanthus | Phyllanthus tenellus |
| Longspine Sandbur | Cenchrus longispinus |
| Lyreleaf Sage | Salvia lyrata |
