Margaret Larkin collected the song from Miss Frances Dwire. Larkin speculates that the name, "Plantonio," was the Spanish Antonio, added to for the sake of alliteration.

PLANTONIO
Margaret Larkin, from Frances Dwire.

1
I'll tell you a story,
There is one I know,
Of a horse I once owned
In New Mexico.
2
Swift as an antelope,
Black as a crow,
Star on his forehead
Was whiter than snow.
3
His arched neck was hidden
By a long flow of mane,
They called him Plantonio,
The Pride of the Plain.
4
The country was new
And the settlers were scarce,
And the Indians on the warparh
Were savage and fierce.
5
The captain stepped up,
Said sommeone must go
For the aid and protection
Of New Mexico.
6
A dozen young fellows
Straightforward said "Here!"
But the captain saw me,
I was standing quite near.
7
"You're good for the ride,
You're the lightest one here,
On the back of that mustang,
You've nothing to fear."
8
They all shook my hand
As I nodded my head,
Rode down the dark pathway,
And north turned his head.
9
The black struck a trot,
And he kept it all night,
And just as the east
Was beginning to light
10
Not a great ways behind
There arose a fierce yell,
And I knew that the redskins
Were hot on my trail.
11
I jingled the bells
At the end of his rein,
Spoke his name softly
And struck his dark mane.
12
He answered my call
With a toss of his head.
His dark body lengthened
And faster he sped.
13
The arrows fell 'round us
Like torrents of rain.
Plantonio, Plantonio,
The Pride of the Plain.
14
I delivered my message,
And tried to dismount,
But the pain in my foot
Was so sharp I could not.
15
The arrow you see
Hanging there on the wall,
Had passed through my foot,
Stirrup, saddle and all.
16
With New Mexico saved
We'd not ridden in vain,
Plantonio, Plantonio,
The Pride of the Plain.

With musical score.
Margaret Larkin, 1931, "Singing Cowboy, a Book of Western Songs," Alfred Knopf; reprint Oak Publications 1963.

The story is told of Wild Bill Hickox riding to the fort at one time, and taking an arrow in the foot. The song bears no relation to any event in New Mexico.