Plants

 Manuals
Ontario
Regional
Habitats
Weeds
Edible
Other

Wildflowers
Ferns
Grasses
Mosses

Ontario Field Naturalist's Toolchest
Manuals
Manual of Vascular Plants of Northeastern United States and Adjacent CanadaIllustrated Companion to Gleason and Cronquist's ManualMinnesota FloraWisconsin FloraMichigan Flora Upper Peninsula
Manual of Vascular Plants of Northeastern United States and Adjacent Canada Am GB
Covers all our vascular plants (woody plants, ferns and grasses but not mosses and their allies).  A comprehensive book that is rather scientific, expensive and recommended only for advanced plant enthusiasts.  
Illustrated Companion to Gleason and Cronquist's Manual GB
The manual of vascular plants is primarily a key and this book provides illustrations to make it easier to use.
Minnesota Flora Am
Wisconsin Flora Am
Michigan Flora Upper Peninsula GB
These three are by the same author, and are of similiar format.  I think these books cover almost all the plant species of each respective state..

An Illustrated Flora of the Northern United States and Canada Volume 1
An Illustrated Flora of the Northern United States and Canada Volume 2
An Illustrated Flora of the Northern United States and Canada Volume 3
An Illustrated Flora of the Northern United States and Canada Volume 1 2 & 3
Text is quite dated but the illustrated are great.  With the number of species covered larger genuses are difficult to key.  Sucks a bit it is spead out over three volumes, but copies can be found cheap.

Links on technical manuals...
Flora of North America  A reference series to all of North America's plamts (USA and Canada), about 2/3 done.


Ontario
Plants of Southern OntairoForest Plants of Central OntarioWetland Plants of Ontario
Plants of Southern Ontario Am
A general plant guide for southern Ontario up to Sudbury, North Bay and Sault St. Marie. Covers trees, shrubs, wildflowers, grasses. ferns and aquatic plants.
Forest Plants of Central Ontario GB
Covers common trees, shrubs, wildflowers, ferns, grasses, sedges, clubmosses, horsetails, mosses,  lichens and more.    There is an edition for Northeastern Ontario as well.  None for southern or western Ontario though.
Wetland Plants of Ontario GB
Similiar to Forest Plants of Cental Ontario but focuses on wetlands and covers all of Ontario.


Regional
The Vascular Plants of Bruce PenisulaThe Flora of Manitoulin IslandVascular Plants of Thickson's Woods
Field, Forest, HedgerowHaliburton Flora
The Vascular Plants of the Bruce Peninsula, Ontario Blog Am
The Flora of Manitoulin Island (third edition) Pub
Vascular Plants of Thickson's Woods Pub A Checklist
Field, Forest, Hedgerow A hiker's wildflower guide for Prince Edward County Pub
Haliburton Flora Archive

Plants Of The Kingston RegionPlants of Quetico and the Ontario ShieldChecklist of Vascular Plants of Thunder Bay District
Plants Of The Kingston Region GB
Plants of Quetico and the Ontario Shield GB 
Two different regional plant guides
Checklist of Vascular Plants of Thunder Bay District Pub

Links for regional...
Southern Ontario Vascular Plant Species List Omits some northern and western species (about 500 out of 3400)  but otherwise a fairly complete list of plants for Ontario.  3rd edition, 2013

Habitats
The Book of Forest and Thicket The Book of Swamp and Bog The Book of Field and Roadside Winter Botany Bogs & Fens: A Guide to the Peatland Plants of the Northeastern United States and Adjacent Canada
The Book of Forest and Thicket GB
The Book of Swamp and Bog GB
The Book of Field and Roadside GB
The coverage of these three books is eastern North America.  These books are not field guides in the conventional sense. Only common plants are covered but the write ups on each plant is superb.  The write ups explores the connections between plants, bugs and their habitats. This makes these books more interesting than typical field guides and is likely to attract interest from bugsters.  
Winter Botany GB
In the wintertime not much is going on in nature so for people interested in plants Winter Botany might cure the winter blues..
Bogs & Fens: A Guide to the Peatland Plants of the Northeastern United States and Adjacent Canada Am

Tallgrass Prairie Wildflowers: A Field Guide to Common Wildflowers and Plants of the Prairie Midwest A Naturalist's Guide to Field Plants A Naturalist's Guide to Forest Plants A Naturalist's Guide to Wetland Plants

Tallgrass Prairie Wildflowers: A Field Guide to Common Wildflowers and Plants of the Prairie Midwest Am
Common flowers seen in tallgrass prairie, an rare habitat in Ontario.
A Naturalist's Guide to Field Plants: An Ecology for Eastern North America GB
A Naturalist's Guide to Wetland Plants: An Ecology for Eastern North America GB
A Naturalist's Guide to Forest Plants: An Ecology for Eastern North America GB

Wetland Plants of Wisconsin Wetland Plants of Michigan A Great Lakes Flora Guide to Great Lakes Coastal Plants

Wetland Plants of Wisconsin Am 
Wetland Plants of Michigan Am
A Great Lakes Wetland Flora Am
Wetland Plants of Minnesota Archive
All by the same author.
Guide to Great Lakes Coastal Plants Pub

Links for habitats...
Lake Huron Coastal Dune Plants Guide The Good, the Bad and the Ugly
PDF
The Big, Bad Book of Botany GB
Astereae Lab All the asters and goldenrods of Ontario and somewhat beyond are covered.  Interestingly a rather new goldenrod species has been described in 2013 and occurs in Ontario -- Brenda's Goldenrod.
Aquatic Plants of Illinois Archive

Weeds
Weeds of North AmericaWeeds of the NortheastWeed ID Guide for Ontario Crops
Weeds of North America Am
Weeds of the Northeast Am
Weed ID Guide for Ontario Crops Pub

Links for weeds...
Common Weeds of Ontario A PDF, Archived book
Ontario Weeds


Edible Plants 
A Field Guide to Edible Wild Plants: Eastern and central North AmericaThe Encyclopedia of Edible Plants of North AmericaA Field Guide to Medicinal Plants and Herbs: Of Eastern and Central North America
A Field Guide to Edible Wild Plants: Eastern and central North America (Peterson Field Guides) GB
The Encyclopedia of Edible Plants of North America GB
A Field Guide to Medicinal Plants and Herbs: Of Eastern and Central North America (Peterson Field Guides)  GB

Other
Go Botany Has a bunch of useful keys for the New England area.  Terms are illustrated as you go.
Michigan Flora - University of Michigan Herbarium A key to plants with photos, compreshensive, technical, no illustrations.  Species profiles are have interesting lore.
Andy's Northern Ontario Wildflowers Has nice habitat pictures and includes info on mosses, fungi, mushrooms, lichen and ferns.  Currently under reconstruction.
LSU Herbaria Loads of stuff.  Keys (lucid), links etc.
CanPlant Filter plants by habitat, and other requirements.  Not necessarily comprehensive.  More for gardeners.
Friends of the Wild Flower Garden Excellent close-up photographs.  Could be used to understand astereae for example.  Partial coverage of species.
Minnesota Wildflowers Good pictures and info on plants. Grouped.
Forestry Images Lots of images of plant species, diseases, silvicultural practices and other stuff
Flora of Northern Alabama, Part 4 Identification keys and photographs of aquatic plants.
A Field Guide to Plant Galls

Northern Ontario Plant Database Extensive, southern limit of coverage is North Bay, Ontario.  Some keys. An excellent primer on plant terminology.  Vegetation type summaries.
Canadian Museum of Nature - Our Collections - Search
University of Guelph Arboretum 
Fowler Herbarium at Queen's University 
North American Network of Small Herbaria

Identification Of Major Fruit Types
The Biota of North America Program Lots of neat maps, but mostly for the United States.  Distribution maps of species.
9 Best Plant Identification App Choices of 2020 Tested and Reviewed I disagree about the top choice PlantNet (of the free apps), it should be iNaturalist. The data that has been generated for PlantNet is lower quality than iNaturalist.  The social network  that reviews records for iNaturalist is much better.  The model of FlowerChecker, Plant Identify and Garden Compass - SmartPlant are interesting because real botantists will identify your plant for a US dollar per identification.  
Forest Forensics A Field Guide to Reading the Forested Landscape GB
Reading the Forested Landscape: A Natural History of Newland Am