A Grammatical Dictionary of Botanical Latin

thrix, gen.sg. trichis (s.f.III), abl. sg. triche, in Gk., the hair, both of man and beast: see (2) trich-, tricho-, -trichus,-a,-um (adj.A), -trichum,-i (s.n.II): in Gk. comp.; = L. capillus,-i (s.m.II), q.v.;

- [moss] Nomen graccae compositionis, apud Apulejum primum occurrens et Polytrichum commune designans, a [polys] multum et [thrix] capillus, propter calyptrae indumentum villosum, (C.Muell.), a name of Greek composition, first occurring [in the writings of] Apulius and naming it Polytrichum commune, from [Gk. polys] ‘many’ and [Gk. thrix] ‘hair, due to the villous hair-covering of the calyptra.

Mimosa chrysothrix, gen. sg. Mimosae chrysothricis, “The name “chrysothrix” refers to the golden indument on the young fruits; Ramalina melanothrix, with black sporogones. “

-thrix, -trichis (s.f. III): in Gk. comp.; -‘hair;’ this epithet is a noun in apposition. It functions as an adjective in an epithet but is declined like a noun irrespective of the gender of the generic name with which it is associated [> Gk. thrix, -trichos, s.f.III the hair, the beard]; see trich-, tricho-, -trichus,-a,-um (adj.A), -trichum,-i (s.n.II): in Gk. comp., hairy or hair-like, -haired, -trichous;

         singular          plural 
Nom.    -thrix          -triches      ‘hair’ (s.f.III) 
Gen.    -trichis        -trichum 
Dat.    -trichi         -trichibus 
Acc.    -trichem        -triches 
Abl.    -triche         -trichibus

- brachythrix, with short hair; callithrix, beautiful hair; chrysothrix, golden hair; melanothrix, with black hairs; microthrix, with small hairs; oligothrix, with few hairs; pyrrhothrix, with fiery hair

Malacothrix; Thelypteris phacelothrix, phacelo-, 'bundle, fascicle'

Note: loss of the aitch (h) in cases other than nominative sg.