HARDLY ANYTHING is more beautiful than the Washington thorn, Crataegus phaenopyrum, which has now come into its full beauty, and which will remain a cheerful lovable little tree until its berries at last disintegrate in April.

Often one wanders about the great parking lot of the Federal Triangle, hoping eventually to find the right passageway to the Museum of American History, and in between curses at the gross incompetence of those who design subway exits without the slightest clue how to get anywhere, once you get out of the thing you might admire the beautiful little thorns.

How they have survived the fumes and the general miasma of this greatest of federal complexes I do not know, and admittedly the specimens there are somewhat scrawny and spavined, but they are better than nothing, and a good bit better than one might have expected from federal planning.

Better examples may be seen on M Street at the side of the National Geographic, just east of 17th Street NW. There used to be a block-long row of them, but now only two or three remain. The Geographic is adding a great annex and in the interests of making a particularly large hole in the ground, the row of Washington thorns near the sidewalk has been cut down. It is unlikely, of course, that anything they put up will be as valuable as what they have cut down, but as civilization blunders about in what is ludicrously called progress, nobody thinks of that.

Shakespeare was right, as usual, when he observed that ere you were born was beauty's summer dead.

The finest display of these thorns that I can think of, now that the Geographic innocents have been slaughtered, is on New Mexico Avenue east of Nebraska Avenue near American University.

The trees are rounded, almost like mushrooms, and they reach 12 to 18 feet in height. You could plant them wherever you think a dogwood or a sourwood or a small flowering crabapple would be right.

The crowns are rounded and very twiggy. The tree is not weeping, or even really pendulous, but the branches weigh down with the clusters of scarlet berries, similar to holly berries.

They color in late September or October, and by mid-November all the leaves drop, so the fruit is beautifully displayed on bare, dark branches. The tree is dazzling against a white marble (or concrete) wall, or against yews, magnolias and other evergreens.

In spring the vivid green leaves are pretty enough as they sprout forth, and the inconspicuous flowers are pleasant, in an elderberry sort of way, about the middle or end of May. But it is the fall and winter, of course, that brings the tree to center stage, as it were.

Often the objection is raised, when the subject of deciduous hollies comes up, that those hollies grow too slowly and do not have attractive foliage, so they are pretty only in the fall. Moreover, their berries fall early in the New Year, so they do nothing for the garden in February and March.

This thorn, however, holds its fruit tenaciously, and the daffodils are in bloom before the fruit withers or loses color or at last falls off the twigs.

There are not many small trees that give no trouble in cultivation, that have handsome shape and foliage, plus pleasant flowers and very showy fruit throughout the dullest season of the year.

I have often thought that if this thorn were not native -- if it came from Assam or Upper Burma -- it would have seized the imagination of all gardeners. Few trees are more fashionable nowadays than one of the Asian maples, Acer ginala, partly because it is an exotic, and partly because the English have been having fits about it for the past quarter-century (and it takes about that long for news to cross the Atlantic).

Also, I suspect the Washington thorn does not do well in the maritime climate of Ireland and England. So many plants from continental climates fail to show their true beauty in mild climates. (Our native dogwood is one of the more conspicuous failures of English gardens, in which it does not flower at all freely; this being the clinching argument against their frightful climate in which the sun never shines at all, and in which everything grows slowly, as in an ice-box).

The Washington thorn is a small tree of the greatest merit, quite equal to the dogwood itself in vigor, beauty, freedom from even slight flaws. It is quite perfect, actually. The reason it is not seen far more frequently is that nurserymen apparently cannot make as much money on it as they do on weedier plants