Laudator Temporis Acti

W.H. Auden, The Epigoni:

No use invoking Apollo in a case like theirs;
The pleasure-loving gods had died in their chairs
And would not get up again, one of them, ever,
Though guttural tribes had crossed the Great River,
Roasting their dead and with no name for the yew;
No good expecting long-legged ancestors to
Return with long swords from pelagic paradises
(They would be left to their own devices,
Supposing they had some); no point pretending
One didn't foresee the probable ending
As dog-food, or landless, submerged, a slave;
Meanwhile, how should a cultured gentleman behave?
It would have been an excusable failing
Had they broken out into womanish wailing
Or, dramatising their doom, held forth
In sonorous clap-trap about death;
To their credit, a reader will only perceive
That the language they loved was coming to grief,
Expiring in preposterous mechanical tricks,
Epanaleptics, rhopalics, anacyclic acrostics:
To their lasting honor the stuff they wrote
Can safely be spanked in a scholar's foot-note,
Called shallow by a mechanised generation to whom
Haphazard oracular grunts are profound wisdom.

This short poem invites lengthy commentary. I'll confine myself to brief remarks on lines 20 ("Epanaleptics, rhopalics, anacyclic acrostics") and 5 ("no name for the yew").

In epanaleptic elegaics, the second half of the pentameter repeats the opening words of the preceding hexameter. In rhopalic verses, the first word is a monosyllable, the second a disyllable, the third a trisyllable, etc. Anacyclic verses can be read and scanned backwards as well as forwards, e.g. these by Publilius Optatianus Porfyrius (Latin Anthology 1.1.81):

Blanditias fera mors Veneris persensit amando,
  Permisit solitae nec Styga tristitiae.
Tristitiae Styga nec solitae permisit, amando
  Persensit Veneris mors fera blanditias.

In acrostic verses the initial letters of each line spell out a word or message—see E. Courtney, "Greek and Latin Acrostics," Philologus 134 (1990) 3-13.

A possible source for "no name for the yew" (line 5) is T. Peisker, in The Cambridge Medieval History, vol. II (New York: Macmillan, 1913), chap. XIV (The Expansion of the Slavs), p. 418:

Until lately the place where the Old Balto-Slavonic branched off from the other Indo-European languages and the place of origin of the Slavs were matters of dispute. But in 1908 the Polish botanist Rostafiński put forward from botanical geography evidence from which we can fix the original home of the Balto-Slavs (and consequently that of the Germans too, for the Balts could only have originated in immediate proximity to the Germans). The Balto-Slavs have no expressions for beech (fagus sylvatica), larch (larix europaea), and yew (taxus baccata), but they have a word for hornbeam (carpinus betulus). Therefore their original home must have been within the hornbeam zone but outside of the three other tree-zones, that is within the basin of the middle Dnieper (v. map). Hence Polesie—the marshland traversed by the Pripet, but not south or east of Kiev—must be the original home of the Slavs. The North Europeans (ancestors of the Kelts, Germans, and Balto-Slavs) originally had names for beech and yew, and therefore lived north of the Carpathians and west of a line between Konigsberg and Odessai. The ancestors of the Balto-Slavs crossed the beech and yew zone and made their way into Polesie; they then lost the word for beech, while they transferred the word for yew to the sallow (Slav. iva, salix caprea) and the black alder (Lithuan. yeva, rhamnus frangula), both of which have red wood.

See also P.M. Barford in Abbott Gleason, ed. A Companion to Russian History (Chichester: Wiley-Blackwell, 2009), pp. 21-22 (footnotes omitted):

Another variant of the loan-words method was linguistic research on the terminology of plants with limited geographical extent. In the 1880s, the Polish botanist and humanist Józef Rostafiński concluded that the Urheimat of the Slavs must have been a region devoid of beech, larch, and yew. This is because all Slavic languages have words of Germanic origin for these trees. Proto-Slavic had, therefore, been spoken outside the range of such trees but in a zone where hornbeam grew, since there was an old Slavic word for hornbeam. Rostafiński concluded on the basis of the distribution of these species that the homeland of the Slavs was the marshes along the Pripet River, near the present-day Ukranian-Belarus border. Many later scholars have also found this "beech argument" enticing. The Urheimat in the Pripet marshes was also endorsed by a number of scholars, among them Max Vasmer, the Russian-born German linguist.