First Person Agents in (h)a- < *wa

[Rankin, Robert L]

> Note that initial *p- is fairly rare in Siouan.  It is mainly restricted
to certain verb stems, mostly formed with *pV-instrumentals, and to *pe
'who' and a few highly irregular sets like 'hill' that smell a lot like
loan words.  The verbs in question were all irregular (syncopating).

If Siouan is related distantly to Caddoan and/or Iroquoian, then the fact that those languages have a paucity of labials may be significant.  On the other hand, I recall that in Uto-Aztecan initial */p/  >  /w/ in some of the languages, even though in initial one would expect the opposite (w>p).  
 
Bob