I may be out on a limb with this... but I actually see two sub-categories of boho, being subtly different while coming from the same inspirations originally.
The more recognizably current boho chic is something that, if I recall correctly, started off in the 1990s and looks back to hippie style. The other, older boho has its sense in early 20th-century socio-political movements, and it is really odd to note *now* that Sherlock Holmes was described as bohemian by his author! Mark Twain considered himself a Bohemian --- and you see overtones of that in Tom Sawyer's attraction to Huck Finn's oppressed, deprived but free life.
That first sense is reactionist --- anti-establishment, *simple* in that it often chooses to do away with structure and layers (in every sense), has a very frugal heart even when accompanied by wealth and luxury. This is, and I hope I do not offend anyone with this descriptor, gypsy-boho. The choc-a-block-ness of detail and ornate elements that seems to belie simplicity likely comes from the gypsy love of embellishment and the highly decorated caravans --- but again, if you look again, there is a very frugal heart to it. There's a bit of a magpie tendency too, right alongside a practical (and paradoxical) minimalism. There is, as well, a certain nostalgic quality to bohemianism --- hence the association of very traditional patterns (paisley) and silhouette (smocks, pinafores, gathered skirts, full slouchy pants). There is a strong sense of artistic patronage too, so that 'artsy' becomes closely allied with boho. This sometimes leads to more avant-garde elements as well, which might eschew the traditional as twee!
In style, this can translate to pre-Raphaelite lushness and naivete (the obverse of curated bombshell sexy), with the hair long and natural, full red mouth, and strong eyebrows, with garments in a luxurious fabrication falling in loose folds, but not a lot of structure and extra embellishment (no corsets and collars) --- but perhaps one eye-catching 'naive' adornment like a flower, a feather or a string of beads. There is sometimes an Orientalist flavour of velvets and silk in dark colours (including black), tassels, braided leather, gold detailing --- and unstructured longer-length garments (rarely is the boho skirt above knee length, or the shirt cropped). This -- to my thinking --- is a more organic and craftsy and tradition-inspired and *sexy* boho than the Flower Power that followed, which emphasized naivete in a sense of child-like innocence rather than lush nature alone. That's where, to my mind, boho acquires more attenuated qualities --- and this is my personal bias, I should disclose --- nearly becomes a caricature of itself.
Freedom from socially imposed restrictions remains a running thread through it all, especially as women's lib takes it up, which likely explains the sheer fabrications and bra-less silhouettes of boho as well --- the idea of eschewing petticoats and muslins. A tomboy element pops up as well in more modern boho, because of course the feminine can itself be an imposition. So shorter hair (Eton crop), girls in pants and a man's oversized shirt...and the pullover and knickerbockers look which I see as an ancestor to the current trend of slouchy pants and loose T-shirt! But the gypsy-inspired alternative of florid corsets and voluminous skirts never does disappear either, a la 'New Look' Dior. Rive gauche and jazz start to feed the image too, hence there comes in sharper tailored androgyny along with an insouciant element --- the Grecian sandal was barely considered a shoe and would be seen as shockingly 'bare' at one time for a person of a certain socio-economic class. This resulted in the cafe-culture bohemian of long political and artistic discussions, wearing the beret and turtleneck with suit and duffel coat --- the icon a male student, but a look and intellectual posture that females would also adopt. This is about the time that the 'jersey' --- T-shirt and sweater material --- starts to become HUGE. The boho as flaneur and louche and iconoclast appear --- and often dress the way you might want to Astrid, in very simple classic shapes, not many layers and not much embellishment because simplicity and frugality are key, but adding a deliberately 'arty' or traditional or political element. This isn't the straightforward naive romanticism of some earlier or later eras, but a more ironic or political adoption.
Greenwich Village beat generation, baby boomers and psychedelia come later (though there was opium before LSD). Just as women's hair went short in emancipation, men's gets long in this anti-war liberation phase --- and a lot of the recognizably boho motifs we now see as 'essential' arrive, quite late in the story really. The peace sign, the paisley, the flower-power garlands, flares, yoga...Herbal appeal in mainstream cosmetics and household products has its roots around here, and of course there is an Orientalist inspiration added to gypsy.
Boho as cafe culture never does go away, of course, just simmers quietly in the corner and possibly glowers at the Beatlemania band. But the Sienna Miller boho, a la Glastonbury (and hence hippie-informed), takes more from the latter phase and thus reinforces --- I strongly suspect --- the idea of boho as a slightly 'stuck' posture (rather than as politics, changing always because reactive) including gilets and furry vests, long flowy skirts, long slightly wavy hair, oversized cardigans over embroidered peasant-ish tunics and blouses, leggings, the hobo bag(!) and oh yes, Uggs! (okay other slouchy boots as well, but also furry boots like the Uggs). This version of boho, I think, has recognizably more bling (India-inspired?) even though it relies heavily on 'folk' elements. And also adds in the flouncy or floaty mini-dress (the smock that has forgotten its nether partner?) as well as a resurgence of tattoos and imaginative make-up (curly eyeliner, painted lids and henna/mehendi art).
The more current boho-inspired looks are hardly spoken of as 'bohemian' by contrast, yet to my eye are strikingly so, especially in the older sense --- the eclectic androgyny of slouchy pants and military jackets on women, sheer and crochet fabrications, the longer-sleeved T-shirt, plaited leather and obi belts, the India-inspired dreadlocked and bejewelled models of the recent Chanel show, flowered Fluevogs and Doc Martens all say boho to me! I certainly think of all of these, plus grunge and gothic, when talking of the boho element in my own style. But possibly not many would agree with this identification or interpretation.
