Ask Mr. Smarty Plants

We don't know about global definitions, but we can tell you what our definitions of some of the terms referring to various plants are:

Sun is 6 hours or more of sun daily, part shade 2 to 6 hours,  shade less than 2 hours of sun a day.

Good drainage means water does not stand on the surface of the soil for more than a few minutes. Especially in our alkaline soil, drainage is very important, and compost added to the soil will help just about any plant. The compost not only enriches the soil and improves its texture, but it helps to make trace elements necessary to the plant available in the soil. If you don't know what your drainage is, dig a hole, run water in it, and if water is still standing in it in about 30 minutes, you probably have clay soil and you definitely have poor drainage. 

Soil moisture refers to the normal condition of the soil when it hasn't been raining or watering has not  just occurred. Most of the soils in Austin would have to be considered dry. 

We recommend plants native not only to North America but to the area in which the plant is being grown, because those plants are already adapted to the climate, rainfall and soils. 

You are correct, while Mahonia trifoliolata (agarita) and Ilex vomitoria (yaupon) have low water requirements and do well in sun or part shade, as well as alkaline soil, Morella cerifera (wax myrtle) needs more moisture and does better in sandy, slightly acidic soil. The wax myrtle, while it will do okay in Central Texas, is more an East Texas kind of shrub. Trying to mix these shrubs in a hedge is going to be a little awkward as the agarita only grows to 3 to 5 ft., 8 ft. under favorable conditions. The yaupon grows from 12 to 25 ft. tall. If you're thinking of building a screen, you might have a problem with the fact that the agarita will not grow nearly as high as the yaupon. All three will serve your desire for attracting wildlife, but not necessarily a uniform hedge.  In general, a "mixed" hedge might be a little harder to care for and not as uniform looking. If you want to make a visual barrier, the yaupon is your best bet. If you want to have a physical barrier, agarita is the thing-it is thick and stickery-trespassing would be painful.

Yaupon and wax myrtle are listed as "dioecious," which means that only the females have berries and there must be a male of the same species, blooming at the same time, within 30 to 40 feet, for the berries to develop. If you had a hedge of 12 yaupons, for example, a couple of males in that hedge would assure berries on the females.

Mahonia trifoliolata

Mahonia trifoliolata

Ilex vomitoria

Ilex vomitoria