The sheer volume of material available on Hawaiian plants is massive. Only a brief overview is provided on this website. Additional information on on this website can be found under the description of Natural Communities, also the page Vegetation, Plant Communities, and Habitats, and several of the pages under the main menu heading of Hawaiʻi’s Unique Biodiversity, including The Extrodinary Evolution in Hawaii and A Look at Some Unique and Amazing Places, Plants and Animals.
Hawaiian Plant Life, Vegetation and Flora by R.J. Gustafson et al. (2014) is an excellent resource as a starting place. It includes natural history information and concise but detailed text descriptions of genera and 2/3 of Hawaiian native plant species along with high-quality photos. A “Further Reading” section at the end of the book has references for each chapter of the book and for all Hawaiian plant families.
The Flora of the Hawaiian Islands (flowering plants only) is available in a hard copy two-volume set but it can also be accessed electronically here: https://naturalhistory2.si.edu/botany/Hawaiianflora/.
A website by Bruce Bohm with an engaging style containing information and photos on many individual species, both native and non-native, organized by plant family is here: https://floridata.com/hawaii/index1.html.
For an evolutionary perspective on the flora of the Hawaiian Islands and islands in general the classic book Island Biology by Carlquist (1974) and the more recent paper special issue in AoB PLANTS is a great resource. See Introduction to the Special Issue: Advances in island plant biology since Sherwin Carlquist’s Island Biology in AoB PLANTS: https://academic.oup.com/aobpla/article/doi/10.1093/aobpla/plv148/2609503.
Below is a table from Imada Hawaiian Native and Naturalized Vascular Plants Checklist (December 2012 update) that summarizes numbers of naturalized, indigenous, and endemic species in the islands: http://hbs.bishopmuseum.org/publications/pdf/tr60.pdf.
Wikipedia lists and has links to many of the endemic plant species in Hawaiʻi: https://en.wikipedia.org/wiki/Category:Endemic_flora_of_Hawaii.
Two lecture slides from a botany class ‘Biogeography of Hawaiʻi’ taught by Ken Systsma at UW-Madison are shown below (the website that had links to these lecture slides is no longer available – removed possibly sometime in 2019). The first lists some of the main Hawaiian plant families and its disharmonic nature (imbalance relative to its mainland source regions) and the second illustrates the extraordinary radiation of plant species. The specific numbers may be slightly out-of-date but the general conclusions are accurate.
Historical ranges for all native Hawaiian plant species were developed and are provided as described in the report Mapping Plant Species Ranges in the Hawaiian Islands—Developing a Methodology and Associated GIS Layers, Price et al. (2012): https://pubs.usgs.gov/of/2012/1192/. The website includes a separate file with a table of all plant species each species with a link to a map and a zip file with all the GIS files.
A 2007 paper by D. Burney and L. Burney ‘Paleoecology and “inter-situ” restoration on Kaua`i, Hawai`i’ (https://pdfs.semanticscholar.org/d122/4dd5a573679d7ea28f7a557cb8e326807c1a.pdf) discusses some practical aspects of plant range information using paleoecologic data and argues for restoration (or rewilding) for some species to include areas where there are not historical records.
The best single source and very informative resource for conservation issues for Hawaiian plants is the Hawaiʻi Plant Conservation Network which is here: https://laukahi.org/. Included there is a plant conservation strategy for Hawaiʻi: http://laukahi.org/wp-content/uploads/2016/02/Hawaii-Strategy-for-Plant-Conservation_AUG-28-2014.pdf (has estimated numbers of individuals of many species).
Other sources include a list and links to descriptions of plants designated as Species of Greatest Conservation Need in the 2015 State Wildlife Action Plan. In that plan are a total of 177 species designated by the Hawaiʻi DLNR (which are given the designation on the website as Genetic Safety Net Species). The link is here: https://dlnr.hawaii.gov/wildlife/hswap/fact-sheets/. The Plant Extinction Prevention Program which focuses on evaluation and restoration of species with less than 50 individuals left in the wild is here: http://www.pepphi.org/.
Photos and basic information on most indigenous Hawaiian plants and organized by genera are here: http://www.botany.hawaii.edu/faculty/carr/natives.htm. The website states that photos can be freely used if for educational or instructional purposes. Thousands of photos of Hawaiian native plants with general locations where found by one of Hawaiʻi’s most knowledgeable botanists, Joel Lau is here: https://www.flickr.com/people/53193377@N02/. Lots of excellent photos are also available here: http://www.starrenvironmental.com/images/.
For illustrations for the various species (versus photos) search here: http://www.plantillustrations.org/.
The Hawaiian Lobelias (Campanulaceae) and Silverword Alliance
For information on these amazing examples of Hawaiian plants and evolution go the this page on the website.
Hawaiian Palms (Loulu)
An interesting study on the only Hawaiian palm genera (Hawaiian name Loulu), Evaluating multiple criteria for species delimitation: an empirical example using Hawaiian palms (Arecaceae: Pritchardia), by C. Bacon, M. McKenna, M. Simmons and W. Wagner in BMC Evolutionary Biology (2012) is here: https://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-12-23. The figure below is from that study.
See also the interesting story with anecdotes about loulu in the Hana Ho Vol.17, no.6 (December 2014 / January 2015 issue). For a captivating video Secret Loulu Forests of Oahu go here: https://vimeo.com/240402843.
Ferns and Fern Allies
Ferns of Hawaiʻi were described in a book by Daniel Palmer in 2003.
Since publication of that book additional work on fern taxonomy has resulted in an online fern flora put together by Daniel D. Palmer and Tom Ranker and it is available here: https://serv.biokic.asu.edu/pacific/portal/projects/index.php?pid=9. Tom Ranker’s website with information on his fern work in Hawaiʻi is here: http://www.botany.hawaii.edu/people/tom-ranker/ and is where you can get a spreadsheet of the updated names of Hawaiʻi ferns and lycophytes. A key to the species of Hawaiian ferns is online is here: https://keys.lucidcentral.org/keys/v3/ferns_of_the_hawaiian_islands/ferns-of-the-hawaiian-islands.html.
Images for some ferns by Tom Ranker are here: https://www.flickr.com/photos/tom_ranker/albums/72157613455204153. Other photos are here: https://hear.smugmug.com/Photographers/HLO/HLOferns/.