Quick answer: 74 native Rhode Island plants have a recorded bloom range that includes May.
74 species
- American basswood Tilia americana · 32 states
- American beech Fagus grandifolia · 24 states
- American cranberry Vaccinium macrocarpon · 2 states
- American holly Ilex opaca · 24 states
- American hornbeam Carpinus caroliniana · 29 states
- American mountain ash Sorbus americana · 18 states
- Atlantic white cedar Chamaecyparis thyoides · 12 states
- Beach plum Prunus maritima · 2 states
- Bear oak Quercus ilicifolia · 1 states
- Birdfoot violet Viola pedata · 14 states
- Black cherry Prunus serotina · 32 states
- Black huckleberry Gaylussacia baccata · 8 states
- Black tupelo Nyssa sylvatica · 19 states
- Black walnut Juglans nigra · 33 states
- Bur oak Quercus macrocarpa · 24 states
- Butterflyweed Asclepias tuberosa · 37 states
- Canada anemone Anemone canadensis · 22 states
- Canadian serviceberry Amelanchier canadensis · 17 states
- Cardinal flower Lobelia cardinalis · 37 states
- Carolina springbeauty Claytonia caroliniana · 8 states
- Chokecherry Prunus virginiana · 35 states
- Cinnamon fern Osmunda cinnamomea · 13 states
- Common blue violet Viola sororia · 21 states
- Common winterberry Ilex verticillata · 10 states
- Common yarrow Achillea millefolium · 31 states
- Creeping phlox Phlox subulata · 11 states
- Downy serviceberry Amelanchier arborea · 34 states
- Dwarf fothergilla Fothergilla gardenii · 9 states
- Eastern red cedar Juniperus virginiana · 36 states
- Eastern red columbine Aquilegia canadensis · 36 states
- Eastern white pine Pinus strobus · 19 states
- Fire pink Silene virginica · 8 states
- Flowering dogwood Cornus florida · 22 states
- Foxglove beardtongue Penstemon digitalis · 31 states
- Gray alder Alnus incana · 12 states
- Highbush blueberry Vaccinium corymbosum · 4 states
- Jacob's ladder Polemonium reptans · 17 states
- Lanceleaf coreopsis Coreopsis lanceolata · 28 states
- Lowbush blueberry Vaccinium angustifolium · 14 states
- Mapleleaf viburnum Viburnum acerifolium · 5 states
- Mayapple Podophyllum peltatum · 18 states
- Mountain witch-alder Fothergilla major · 7 states
- Nannyberry Viburnum lentago · 23 states
- New Jersey tea Ceanothus americanus · 31 states
- Northern red oak Quercus rubra · 24 states
- Northern spicebush Lindera benzoin · 16 states
- Pagoda dogwood Cornus alternifolia · 25 states
- Partridgeberry Mitchella repens · 17 states
- Pitch pine Pinus rigida · 12 states
- Post oak Quercus stellata · 9 states
- Red baneberry Actaea rubra · 22 states
- Red chokeberry Aronia arbutifolia · 7 states
- Red pine Pinus resinosa · 13 states
- Red-osier dogwood Cornus sericea · 22 states
- Royal fern Osmunda regalis var. spectabilis · 8 states
- Sassafras Sassafras albidum · 22 states
- Scarlet beebalm Monarda didyma · 18 states
- Scarlet oak Quercus coccinea · 17 states
- Shagbark hickory Carya ovata · 22 states
- Sugar maple Acer saccharum · 28 states
- Sundial lupine Lupinus perennis · 25 states
- Swamp rose Rosa palustris · 11 states
- Sweet birch Betula lenta · 18 states
- Sweet-fern Comptonia peregrina · 10 states
- Sweetgum Liquidambar styraciflua · 22 states
- Tulip tree Liriodendron tulipifera · 17 states
- Twoleaf miterwort Mitella diphylla · 7 states
- Virginia creeper Parthenocissus quinquefolia · 27 states
- Virginia springbeauty Claytonia virginica · 10 states
- White ash Fraxinus americana · 31 states
- White baneberry Actaea pachypoda · 16 states
- White oak Quercus alba · 33 states
- Wild blue Phlox divaricata · 32 states
- Willow oak Quercus phellos · 16 states