Article (magazine)  (Jan 1955)  Page(s) 13.  
 
There were also hundreds of lilac pinks, magenta. pinks and plain magentas, most of which were very unattractive. Many closely resembled Banksi. Typical varieties were 'Archduc Ludovico,' 'Athlete,' 'Beaute de Twickel,' 'Jules PirIot,' 'La Ville de St. Denis,' 'Morris,' 'Princess Louise,' 'Reine Amelie,' 'Reine des Fleurs,' 'Triomphe de Vandermaelen,' and 'van Houttei.' All these varieties proved, in Holland and France, easy to propagate in comparison with the later introduced Japanese varieties. Which varieties bearing European names were actually raised from seed in Europe and which were Chinese varieties renamed is not too definitely established.

Website/Catalog  (1924)  Page(s) 152.  
 
Pivoines en arbre...Triomphe de Van der Maelen.- Grande, pleine, rose violacé vif.

Book  (Apr 1907)  Page(s) 85.  
 
876. FLANDRES, TRIOMPHE DE ; P. moutan....
(1) 1906, Dessert's Cat. p. 43.

Website/Catalog  (1906)  Page(s) 37.  
 
Paeonia arborea. Tree-Peonies. A selection of especially fine double sorts.
Van der Maelen, light violet, centre cherry-red, densely filled.

Website/Catalog  (1893)  Page(s) 42.  
 
Tree Pæonies.  Pæonia Arborea.
This beautiful group of shrubs is among the oldest of introductions from Japan, but magnificent new varieties have been added from year to year until we have a long list of wonderful forms.  They are quite distinct from the herbaceous section, and have shades of color not found in the latter; and when once established form compact bushes, which in spring are covered with the gigantic blooms.  These pæonies are a little tender in exposed situations north of Boston; but if planted in a sheltered, warm location, and protected during the first two winters by a covering of pine boughs, or other loose material, will eventually establish themselves, and form one of the most decorative features of the garden.  Like the herbaceous kinds, they enjoy rich soil, and the blooms last longer and come finer when partially sheltered from the hot sun.  They are well worth the little trouble entailed in their cultivation.  We can offer strong plants of the leading and most hardy kinds; but as they are slow and difficult of propagation, this fact will account for their relatively higher cost over the herbaceous kinds.  Having secured a large stock of these beautiful plants, we are enabled to offer them at lower prices than ever before.  2 year plants, 75 cents each; 3 year plants, $1.00 each.
Triomphe de Vandermalaen.  Enormous flower, incurved, perfectly formed, purplish rose; centre darker shade.

Magazine  (22 Jan 1887)  Page(s) 77.  
 
The Tree Pæony. 
...For the last twenty years or longer we have had to look to our French neighbours for new sorts of Tree Pæony, for since they have taken the work of hybridising and raising seedlings in hand they have supplied us with all the finest sorts.  Until now the list is long- too long, in fact, for names are given where very shadowy differences exist.
List of select Varieties.
Triomphe de Vandermaelen, rich violet

Book  (1882)  Page(s) 616.  
 
P. triomphe de Vandermaelen, grosse fleur rouge pourpre.

Magazine  (Jan 1879)  Page(s) 22.  
 
A l'exposition universelle de Paris en 1878
Les nombreux lots de Pivoines sous-frutescentes ou herbacées étalaient leurs larges corolles; les lots de MM. Levêque, d'Ivry; ceux de MM. Verdier, A. Roy, Delahaye et Thièbaut, de Paris, Simon et Crousse, de Nancy, Margottin et veuve Durand, de Bourg-la-Reine étaient très remarquables.
Nous citerons, parmi celles dites en arbres, les variétés suivantes:  Ville de Saint-Denis, Marie Rattier, Souvenir de Madame Knoor [sic], Elisabeth, Comte de Flandre, Louise Mouchelet, Madame de Vatry, Rinzi, Farezzi, Triomphe de Vandermaelen, Mariana, Rossini, Rubra odorata et Athlète.

Magazine  (26 Feb 1876)  Page(s) 197.  
 
The Best Tree Peonies.
The following list contains some of the very best varieties of tree Peonies or Moutans at present in cultivation; I obtained it from my friend M. Charles Verdier, of Paris, who makes Peonies his special study; among them, as will be seen, are few novelties, but M. Verdier states that the newer varieties are generally inferior to the older kinds:
Triomphe de Vandermaelen, very large, and double violet-shaded rose...

Book  (1867)  Page(s) pl. 54.  Includes photo(s).
 
PAEONIA MOUTAN sims
(var. Triomphe de van der Maelen.)

Deze Pioen is geteekend naar een exemplaar uit de kweekerij van den Heer C. Glijm te Utrecht , en , als verscheidenheid, van Belgischen oorsprong. Evenals de onlangs door ons afgebeelde , behoort ook zij tot de boom-Pioenen. Bijzonderheden vallen haar aangaande niet te vermelden. Uit onze plaat blijkt reeds genoeg , dat zij door groote , goed gevulde bloemen uitmunt , en aan liefhebbers van Pioenen wel kan worden aanbevolen.

Translation:
This peony is drawn from an example in the nursery of Mr. C. Glijm in Utrecht, and is a variety of Belgian origin. As recently shown by us, it belongs to the Tree Peonies. Specifics are not to be mentioned here. From our plate it is clear enough that it excelks in large, well double blooms and can be recommended to fans of Peonies.