A Grammatical Dictionary of Botanical Latin

Nixus,-us (s.m.IV): a pressure (the same as nisus,-us (s.m.IV), q.v.); a striving, exertion, effort; pains, throes, travail (of parturition); Nixus, a constellation (Lewis & Short)[> L. nitor, infinitive niti, nisus sum or nixus sum 3. deponent: strain, struggle; see nitens,-entis (part.B)].

NOTE: not nexus,-us (s.m.IV, a binding, joining; from necto,-xui or nexi, nexum to bind, join, bind, connect.

In Latin, nīxus means pressing downward, leaning upon, struggling, or striving. It is the perfect active participle of the deponent verb nītor (to lean, push (downward), or strive). When used as a fourth-declension noun, it means effort, labor, or the throes of childbirth.

NOTE: “(Lat., an effort), affinity, as of one species to another of the same genus” (Jackson); affinity: a relation between biological groups involving resemblance in structural plan and indicating a common origin (Miriam-Webster] also likeness based on relationship or causal connection (Miriam-Webster).

Nixus Plantarum : The Tendencies/Strains of Plants: a strain = lineage, ancestry; an inherited or inherent character (Miriam-Webster).

Nixus Plantarum [The Tendencies of Plants] of 1833 by John Lindley: “This was an attempt, in imitation of Agardh and Bartling, to reduce the Natural Orders into groups subordinate to the higher divisions. Such groups were called “Nixus” (tendencies).” “...[Lindley] maintained that no sections are capable of being positively defined, except such as depend upon physiological peculiarities; and that all other collections of species, by whatever name they are known, whose distinguishing marks are dependent upon structure alone, merely exhibit tendencies to resemblance in certain points, for which tendencies definitions are impracticable” (John Lindley: “Natural Systems.” Preface to John Lindley’s: The Vegetable Kingdom of 1846).

Note: the Introduction to the Natural System, of Lindley “was originally written in illustration of the popular system of De Candolle; but daily experience showed the insufficiency of that system ...’ (Lindley 1846).