There is the gregarious D major Quartet, Op. 44, No. 1, and there is the much-talked-about E minor Quartet, Op. 44, No. 2. The String Quartet No. 5 in E flat major, Op. 44, No. 3, might sometimes seem like the odd man out, but there is no need to worry on its account; for, while Mendelssohn is unlike other top-billing composers in that the majority of his works are not standard repertoire fare, this quartet has been standard fare, at least since the revival of interest in Mendelssohn quartets during the mid-twentieth century. The E flat major Quartet was composed in late 1837 and early 1838 (February 6, 1838, is the official date of completion, as duly noted by Mendelssohn on the manuscript), after Op. 44, No. 2, but before Op. 44, No. 1, and was first played -- as usual, by Ferdinand David and friends -- on April 3, 1838. Mendelssohn tinkered with some of the notational details a bit, and it was printed in the early summer of 1839.
Sonata-allegro -- scherzo -- slow movement -- finale is once again the layout selected by Mendelssohn for the quartet (the same blueprint was used for the other Op. 44 pieces), and once again Mendelssohn opts not to preface the quick first movement with a slow introduction, as he had done in his first two string quartets (Opp. 12 and 13). Listen, in the opening Allegro vivace, to the way that Mendelssohn allows the players to take the initial four-note pickup idea and toss it about among themselves -- here in imitation, here by string multiple copies of it together, back-to-back -- as the movement unfolds. Set against this always forward-looking idea are stalwart dotted figures that do their best to keep the apparently boundless kinetic energy of the pickup figure in check, but do not always succeed.
The scherzo (Assai leggiero e vivace) is a particularly nimble example of its breed, even by Mendelssohn's standards. Only at the very end do the constant 6/8 time eighth notes stack up in all four parts into a thick, juicy climax; the rest of the time they are shared throughout the ensemble with remarkable equanimity (though, not surprisingly, the first violinist has a little bit of an edge).
Mendelssohn may have been an aristocratic pseudo-traditionalist, but he certainly knew a good dissonance when he heard one -- and there is a delightful one at the very opening of the A flat major Adagio non troppo, a use of simultaneous chromatic inflections, repeated each time the main melody is begun afresh. By contrast, the Molto allegro con fuoco (and he means it!) is a whizz-bang finale that expects a great deal from the first violinist's fingers.