Scientific: Pyracantha hybrids (a complex scene of horticultural hybrids)
Common: Called 'firethorn' or just plain 'pyracantha', the five most popular species, scarlet firethorn (Pyracantha coccinea), Formosa firethorn (P. koidzumii), Roger’s firethorn (P. rogersiana), Chinese firethorn (Pyracantha fortuneana, Pyracantha crenatiserrata is a synonym), and Pyracantha angustifolia. There are many cultivated hybrids of these species that vary mostly plant size, fruit size and fruit color.
Family: Rosaceae (rose family)
Origin: Eurasia. Collectively, the five species of Pyracantha are broadly distributed from the eastern Mediterranean region and central Europe across to Asia to China and Taiwan (formerly Formosa)

Hardiness zones:
Sunset 4-24
USDA 7 - 11

Landscape Use: Varied depending on cultivar; ground cover, espalier, topiary, informal hedge, background, winter and spring accent, barrier plant, topiary

Form & Character: Evergreen, stiff and upright to spreading

Growth Habit: From prostrate and spreading to rounded or columnar, depending on cultivar. Growth rate of vigorous cultivars is very rapid.

Foliage/texture: P. coccinea has ovate leaves that taper to an acuminate tip, serrate to dentate, to 1.5' long when mature, new foliage can be densely pubescent. P. koidzummii, has lighter green leaves, oblanceolate to espatulate to 2" long, leaf tips are rounded to slightly emarginate. Both species often have the presence of a stipular thorn on a smooth dark brown stem and are plants of medium texture.

Flowers & fruits: Corymbs of small white perfect flowers on terminal meristems in spring followed by clusters of green turning orange to bright red fruits (fruits are actually small pomes, not berries as commonly referenced) in fall and early winter. Fruit color of P. coccinea is scarlet red, 1/4" in diameter. Fruit color of P. koidzummii is orange-scarlet, 1/4" in diameter with head of fruit somewhat flattened.

Seasonal color: White flowers in Spring and orange or red fruit in late fall/early winter.

Temperature: Tolerant

Light: Full sun, but no full western exposures.

Soil: Iron chlorosis in highly alkaline, wet soils is the biggest problem in Phoenix.

Watering: Mostly regular irrigations in southwest deserts. Little to no supplemental water needed along California coastal valleys or in the southeast US.

Pruning: Selectively remove off new growth in mid spring after flower and again in early to mid-fall to reveal and expose fully the fruits for late fall and early winter accent display. Also be careful to selectively remove any growth of the vigorous seedling rootstock in the case of grafted cultivars.

Propagation: cutting, cultivars are usually grafted onto vigorous seedling.

Disease and pests: The bacterial disease fireblight is Pyracantha's biggest problem. Aphids and spider mites also occur.

Additional comments: Many hybrids and cultivars of varied form and fruit color. Specify firethorn or Pyracantha in the landscape by cultivar name. Desirable hybrids and cultivated varieties include:

‘Apache’ grows to 5 feet high and 6 feet wide and has large, bright red fruits that last well into winter. This selection is resistant to fire blight and scab.

‘Fiery Cascade’ grows to 8 feet tall and 9 feet wide, has orange frutis that turn red during the winter and has good disease resistance.

‘Gnome’ is very cold hardy and grows to 6 feet high and 8 feet wide. The fruits are orange. This selection is very susceptible to scab.

‘Lowboy’ is a spreading plant, which reaches a height of only 2 to 3 feet. The fruits are orange, and this selection is also prone to scab.

‘Mohave’ grows to 12 feet tall and wide and has many, big orange-red fruits, which last well into winter. This selection is resistant to fire blight and scab.

‘Teton’ is very cold hardy and grows to 12 feet high and 4 feet wide. The fruits are golden yellow. This selection is also resistant to fire blight and scab.

‘Tiny Tim’ is a compact plant to 3 feet high with small leaves and few or no thorns. The fruits are red.

One of the myths about firethorn is that the fruits are poisonous. If you've ever watched birds feast on firethorn fruits, then perhaps you have wondered if they were indeed poisonous. Birds will simply devour the delicious ripe fruit and might become intoxicated if the fruit is over ripe (containing a bit of alcohol). Ingestion of over ripe fruit will cause birds to do all sorts of weird, stupid stuff such as fly into windows, drop off perches and power lines, or chirp endlessly.

The fact is, Pyracantha frutis (little apples) are entirely edible and there is at least one recipe I've discovered for Pyracantha jelly. If you have a surplus of Pyracantha berries in the fall/winter and would just as soon the birds did not rob you of them, you might enjoy the taste of Pyracantha jelly. It is quite tasty, much like apple jelly in appearance and flavor.

Here is a recipe for you aspiring chefs:
To extract the juice, boil a pound of fruits in 3/4 cup of water for one minute. Strain the juice through clean cloth. To one cup juice, add one teaspoon lemon juice and package powdered pectin. Bring it to hard boil; add 3/4 cup sugar and continue rolling boil 1 minutes, stirring constantly. Pour into hot, sterilized jars.