Quick answer: 39 native North Dakota plants have a recorded bloom range that includes May.
39 species
- American basswood Tilia americana · 32 states
- American bittersweet Celastrus scandens · 11 states
- American hazelnut Corylus americana · 16 states
- American plum Prunus americana · 25 states
- Bearberry Arctostaphylos uva-ursi · 16 states
- Broadleaf cattail Typha latifolia · 11 states
- Bur oak Quercus macrocarpa · 24 states
- Canada anemone Anemone canadensis · 22 states
- Canada wild rye Elymus canadensis · 18 states
- Candle anemone (thimbleweed) Anemone cylindrica · 5 states
- Chokecherry Prunus virginiana · 35 states
- Common blue violet Viola sororia · 21 states
- Common hackberry Celtis occidentalis · 15 states
- Creeping juniper Juniperus horizontalis · 10 states
- Eastern hop-hornbeam Ostrya virginiana · 18 states
- Eastern red columbine Aquilegia canadensis · 36 states
- Golden alexanders Zizia aurea · 12 states
- Gray alder Alnus incana · 12 states
- Gray dogwood Cornus racemosa · 8 states
- Green ash Fraxinus pennsylvanica · 23 states
- Heart-leaved meadow parsnip Zizia aptera · 8 states
- Highbush cranberry Viburnum opulus var. americanum · 8 states
- Indigo bush Amorpha fruticosa · 16 states
- Jack-in-the-pulpit Arisaema triphyllum · 14 states
- Large penstemon (shell-leaf beardtongue) Penstemon grandiflorus · 8 states
- Nannyberry Viburnum lentago · 23 states
- Narrow-leaf coneflower Echinacea angustifolia · 9 states
- Old man's whiskers Geum triflorum · 8 states
- Purple meadow-rue Thalictrum dasycarpum · 7 states
- Quaking aspen Populus tremuloides · 24 states
- Red baneberry Actaea rubra · 22 states
- Red-osier dogwood Cornus sericea · 22 states
- Richardson's alumroot Heuchera richardsonii · 8 states
- Rocky Mountain bee plant Peritoma serrulata · 22 states
- Silver buffaloberry Shepherdia argentea · 11 states
- Smooth Solomon's seal Polygonatum biflorum · 13 states
- Smooth sumac Rhus glabra · 34 states
- Virginia strawberry Fragaria virginiana · 8 states
- Whorled milkweed Asclepias verticillata · 6 states