Tragopogon is a rather critical genus as far as its taxonomy is concerned.
Here in the Mediterranean there are at least two other species resembling T. porrifolius L., T. eriospermus Ten. and T. cupanii Guss. ex DC., the latter endemics to some southern Italian regions.

For a rather long time T. porrifolius and T. eriospermus have been confused. Instead, despite both having "purple" flowers and inflated scape below the capitula, the two species are rather easily distinguished:

• T. porrifolius: 1) ligules maroon , very short, less than 1/2 of phyllaries; 2) phyllaries slightly reflexed at flowering; 3) achene body slightly narrowed into rostrum; 4) leaves strongly undulate at margins; 5) growing in dry habitats:
  https://www.inaturalist.org/observations/115326371

• T. eriospermus: 1) ligules violet, longer than 1/2 of phyllaries and up to as long as phyllaries; 2) phyllaries porrect at flowering; 3) achene body strongly narrowed in a very narrow rostrum; 4) leaves not undulate at margins; 5) growing in wet habitats:
  https://www.inaturalist.org/observations/115324011
  https://www.inaturalist.org/observations/100764720

Here the original description of T. eriospermus and the first drawing:
http://www.ortobotanico.unina.it/FN/TV/TV0176.PDF
http://www.ortobotanico.unina.it/FN/TavoleFN/t0186.PDF

The type of T. porrifolius has been selected here:
https://www.jstor.org/stable/1222832
and can be viewed here:
https://linnean-online.org/9553/

Most of the observations of T. porrifolius from North America refer to another taxon that is more similar to T. eriospermus:
https://www.inaturalist.org/observations?place_id=97394&taxon_id=54141

In Europe it is just slightly better...

Maybe could it be worth revising the presence of the "purple-flowered" Tragopogon in North America?
To do this, apart photographing the capitulum and the scape below the capitulum, it would be useful to photograph:

1) leaves: undulate/not undulate at margins

2) phyllaries: reflexed/porrect at flowering

3) achenes when dried: achene body strongly narrowed into a very narrow rostrum or just slightly narrowed

4) habitat: dry or rather wet

Malva sylvestris vs multiflora vs nicaeensis vs parviflora

1 - Epicalyx united at least in lower half. Petals 12-25(30) mm long, 2-3 times as long as calyx; with purple or deep pink stripes over a lilac background. Fruits smooth or slightly rugose. At least in part often somehow greysh-green due to the presence to rather abundant stellate hairs. Annuals: Malva multiflora (=M. pseudolavatera)
1' - Epicalyx pieces separated. Petals 2,5-30(35) mm long, shorter than calyx or up to 5 times as long as calyx; whitish or tinged with rose in upper half or with purple or deep pink stripes over a lilac or pink background. Fruits reticulate or smooth. Plants green with simple or bifid hairs (M. nicaeensis, M. sylvestris) or green with few scattered stellate hairs (M. parviflora) or with up to rather dense stellate hairs (M. neglecta). Annuals or perennials: 2

2 - Petals 15-30(35) mm long, up to 5 times as long as calyx, with purple or deep pink stripes over a pink background. Perennials: M. sylvestris
2' - Petals 2,5-12 mm long, shorter or up to twice as long as calyx, whitish or coloured with rose in upper half. Annuals (rarely parennials in M. neglecta): 3

3 - Petals 2,5-5 mm long, shorter to slightly longer than calyx, completely whitish or faintly rose-coloured at apex and without pink stripes. Calyx distinctly accrescent at fructification. Stem subglabrous: M. parviflora
3' - Petals 6-14 mm long, 1,2-twice as long as calyx, totally white or with faint pink stripes over a white or very light pinkish background or with pink stripes over a whitish background and pinkish at apex. Calyx not accrescent at fructification. Stem rather densely hairy: 4

4 - Petals with pink stripes over a whitish background and pinkish at apex, rarely whitish and with faint stripes. Fruits strongly reticulate, more often glabrous, rarely hairy. Epycalix pieces ovate or oblong-ovate, relatively broad and close to each other. Plants more often erect: M. nicaeensis
4' - Petals totally white or with faint pink stripes over a white or very light pinkish background. Fruits smooth or slightly reticulate, densely hairy. Epycalix pieces linear or narrowly lanceolate, narrow and distant from each other. Plants more often prostrate or decumbent: M. neglecta