Well, Texas is a good ways from the equator. It doesn't get nearly as hot on a regular basis as say places in Africa would. Actually there's a lot of gardeners that plant plants from Africa. Even though it doesn't get as hot here as in places in Africa or other areas near the equator, we can grow things from those regions. It's funny, though, because we also have stuff in the yard that grows in much cooler climates. Irises for an example, our yard is full of them and they're lush and green and thriving. Infact, I need to thin them out in one flowerbed because they've done so well there. I had planted just a few 3 years ago and now they're just about filling in the flowerbed completely. I took them from another "flowerbed" just a stretch of them alongside the house in the front. I moved them from there since I rarely got to enjoy them because of where they were, kind of hidden from sight.
Irises actually originated in the mountains in China as many popular cut flowers did. They can grow just about anywhere, from cool and cold to downright hot. They're really amazing since they don't freeze in the winter, and thrive and I mean really thrive in sun to partial sun. I've found that they can tolerate temps down to 20F atleast, and temps as high as 105F+. The heat never seems to bother them, I swear they're indestructable. They're a bulb rooted plant. Long light green leaves, sort of like grass. They bloom during the early spring. We have white ones, but they come in several diffferent colors, blue, purple, yellow and a mix color of yellow and purple. I think there's also an orange color.
As for other cooler climate plants, sure we have them. Maples don't really grow like crazy around Austin. But up around Dallas they do have a lot of Maples. We have more Pecans, Elms and many varieties of Oaks. We have sycamores, cypress, pine, cedar, juniper, even palm trees do ok here. It's pretty rare to have anything here that actually dies from the heat, even stuff that grows farther north. If you water a plant enough it'll be ok. Put it in the shade of course. Water is good.
Unless of course it's some kind of plant that can't handle a lot of water, then that might be a problem.
Austin sits in the middle of two different climates and topographies. The west side of Austin is very hilly, with some gentle hills throughout the city. Most of the bigger hills are to the west, though. West of Austin out in the hill country the elevation increases by 1,000+ feet. Areas of the western hill country actually hit 3,000+ feet above sea level, compared to Austin and Travis County which ranges from 350 to 1,400 feet. East of Austin the elevation decreases of course as you get closer to the coast. The terrain becomes flat with some rolling hills between Austin and Houston. But once you're near Houston it's quite flat. Anything down along the coast from Mexico to Louisiana is also very flat. Austin sits just east of the Edwards Plateau and Balcones Escarpment. This is actually an ancient fault line. Infact there's even some extinct volcanoes in the area, atleast two of them within the city limits of Austin.
Climate-wise west of Austin you have a dryer climate. 10 minutes west of the city you can find huge patches of prickly pear cactus growing wild along the highway. There's Yucca cactus. The terrain is of course hilly and rocky with grasses and small bushy type trees. Mesquite
trees grow wild there as do cedar, juniper and oak trees. There's other kinds also, but those are the major ones. During the summer months this is the hottest area of Central Texas with 100+ temps regularly. East of Austin the climate is more humid. It rains more often and is more flat coastal plain, with fields of green grass. Some of the areas between Austin and Houston are beautiful with pine forests. Temperatures there can still get hot, but not nearly as hot as to the west. The thing is the humidity is much worse being closer to the coast.
To the north of Austin it's actually very flat with only small bushy trees. A lot of farmland actually. It's strange, once you get north of the city into the suburbs of Round Rock and Georgetown, up in Williamson and Bell Counties, it's quite flat. South of Austin is different, it's beautiful with rolling hills and thick lush small trees, mostly cedar and oaks. Hays County is really one of the most beautiful areas of Central Texas, especially on its western edge. Farther south in Comal County is also hilly, and then Guadalupe, and then Bexar County, which is where San Antonio is. All of those areas are hilly, especially from the central area of those counties to their western borders.
Hays County - There's a nice picture of Hays County here.