There is a lot of information out there about weaving, crocheting and knitting, but relatively little about spinning.
Which is a shame, since spinning is really where the "resource provided by the earth" tangibly becomes "object with a use."
Aspects of spinning, such as the amount of twist and the length of the fibers, are impactful upon the thread or yarn created, but lots of fiber crafters don't get to directly play with those variables...
It is so strange how textile production is so utterly dominated by very few fibers, when so many are possible. Industry keeps coming up with new ways to transform bamboo or something into fibers, which is all well and good, but we have yet to run out of easily usable natural fibers that have worked for thousands of years.
Dogbane—Apocyonum cannabinum—was called "Indian hemp" because it was used by Native Americans for ropes, cords and textiles. It's incredibly strong, soft, and easy to collect large amounts of it. But hardly anybody uses it.
As far as yarn construction (twist, fiber staple, ply, draw, etc) goes, may I recommend the Spinner's Book of Yarn Designs (Sarah Anderson) and Yarnitecture (Jillian Moreno)? @dirtypuzzle mentioned SpinOff and Fibershed in the comments and those are great magazines and ways to find local groups as well. I've read some great articles on prepping and spinning flax, hemp, cotton, and silk on there in addition to the more popular fleece/fur/hair fibers.
For those especially I can't over-recommend the Fleece & Fiber Sourcebook or the Field Guide to Fleece (Deborah Robson and Carol Ekarius.) An awful lot of excellent fiber breeds and species are now unknown, under-used, and in danger of going extinct; Shave 'Em to Save 'Em and the Livestock Conservancy in general are good resources for finding local people working with those. There's a chiengora (dog wool) group on Ravelry that's great, too, and lots of easily searchable info on raising silkworms at home and spinning from hankies.
There really is a dearth of information easily available on most plant fibers, I too would love to see more of it for like... almost everything, really. At a guess, most potentials get ignored at an institutional level because they're a pain to grow and process in bulk, which in turn means there's little if any data on how they stand up to modern washing and drying and detergents. Bast fibers tend to be a pain to prep as an interested individual (and often smelly!) and can be hard on the hands while spinning, especially those with extra long fibers. Even so a lot of people would spin old/new/ignored plants if they didn't have to process raw plant into spinnable fiber. I suspect that and not knowing which plants might be good options are the biggest obstacles to at least hobbyist experimentation.
Here's a blog post where someone attempts to process and spin milkweed stalks. Keep in mind, milkweed stalks produce a bast fiber whereas milkweed fluff can also be spun but makes a brittle yarn by itself and is often mixed with wool or cotton, though I would assume you could process the stalks and then spin the floss into the fiber from the stalks. Spin Off talks about it here. Milkweed also sustains monarch butterflies, which have been having a rough time. You might have some skin reactions when handling milkweed though, so keep an eye.
Fibershed did a spotlight on dogbane, nettle, and milkweed in comparison to hemp and flax. They talk specifically about Native American techniques and current cultivation of all three, particularly dogbane, and ways to spin yarn and make rope. They aren't super in-depth about processing the fibers, but it seems like it's because they have more tutorials/guides on other pages. Bast fibers all have a similar retting->drying->scutching->hackling->spinning (you also have to ripple flax at the beginning) process, generally speaking.
Of course, flax is a really accessible plant fiber to spin yourself! You can plant it yourself, buy unprocessed flax (locally or online), or buy processed but unspun flax. If you're interested in the whole process, this book is the flax bible: Linen: From Flax Seed to Woven Cloth by Linda Heinrich. There are a lot of youtubers who go through it all, too.
If you're interested in kudzu, then may I suggest Oigawa Kudzu-fu Studio! They're located in Japan, but they have helpfully created an English website, too, where they go over making kudzu-fu (Japanese name for the cloth from kudzu). And if you ever find yourself going to Japan, you can take a class from them.
On Oigawa Studio's info page, they also mention that they work with ramie (plant in the nettle family), linden tree (basswood), and wisteria, so do with that what you will. I assume a lot of those resources are in Japanese.
Finally, hemp. Laws around if and how you can plant hemp, even for personal non-THC uses, vary wildly from state to state and country to country, so do your research. I'm not super familiar with it, and in my state I literally can't grow any of it at all without applying for a permit, so it's not really worth it for me.
To the previously mentioned sources I would add Abbey Franquemonty's
Respect the Spindle. Anyone looking for the how's & why's of hand spinning will find answers there. Interest in hand spinning has seen a steady growth in the past 15 yrs since this book's release.
We live in an era where there is a wide availability in tools, raw materials, and instructions. Before 2005 the spinner-wannabe was hard pressed to find the tools & fiber to even become a spinner much less explore the nuisance of rare fibers.
