Newsletter  (Feb 2020)  Page(s) 22.  
 
[From "The Flowering of Sir Cedric Morris", by Darrell g.h. Schramm, pp. 21-23]
Rosa mulliganii deserves some consideration here. Probably it's a form of R. rubus, or R. longicuspis, or both. When botanist Forrest sent it to the Garden at Wisely in the UK, no one, once it was flourishing, could identify it. The assistant director Brian Mulligan sent material to Belgian rose species authority G.A. Boulenger who identified it as a newly found species, publishing its description in 1937 and naming it for Mulligan. It wasn’t long before the rampant rose was growing on an arbor in the center of the White Garden at Vita Sackville-West’s Sissinghurst. Clearly Cedric Morris was also enamored of this wild rose and planted it in his garden

Book  (2016)  Page(s) 244.  Includes photo(s).
 
Rosa longicuspis has long been confused in commerce and in the literature with Rosa mulliganii, which it resembles very closely. In fact, it has been thought by some authorities to be synonymous, but some distinguishing features for Rosa mulliganii have been reported such as greater maximum height and greater hardiness. My plant grows at least 45 feet (13.7 meters) into a native maple tree. The greatest height record I can find for Rosa longicuspis is 30 feet (9 meters), and the most commonly reported height is 20 feet (6 meters9. It would probably be best to view Rosa mulliganii as a variety or form of Rosa longicuspis.

Magazine  (2007)  Page(s) 5-6.  
 
In "A Tale of Three Great Plants (and Seven Plant Collectors)" by Carolyn Jones, director/curator of the Elisabeth Carey Mill Botanical Garden, reprinted by greatplantpicks.org:
A vigorous rose, which can grow 40 to 60 feet if trained into a tall evergreen, Rosa mulliganii thrives in the maritime climate of the Pacific Northwest. This drought-tolerant rose produces large, fragrant clusters of small white flowers in early summer.

[A] rose... was growing at the Royal Horticultural Society’s (RHS) Garden at Wisley, England. This rose was of particular interest to Brian Mulligan, the Garden’s assistant director. As it did not match any species that Mulligan knew, he sent material from it to G.A. Boulenger, a Belgian botanist specializing in roses. Boulenger—who had written in three parts, between 1933 and 1936, Revision des Roses d’Asie in the Bulletin: Jardin Botanique de l’Etat Bruxelles—was well qualified to comment on this rose sent by Mulligan. Indeed, this was a new species, which Boulenger published (in the same Bulletin in 1937) and named for the sharp-eyed Mulligan. The original species description ... spelled the name Rosa mulligani. The current, correct spelling of the specific epithet is mulliganii.

Mulligan is, of course, known to all concerned with Washington Park Arboretum,for he became part of the fiber of the organization. Blessed with long life, Mulligan spent over 50 years working at the Arboretum— 26 of these as its salaried director and 24 as a volunteer, when times were tough. A quick summary of his life, for the record, completes this tale. He was born in Northern Ireland, northeast of Belfast, in 1907. He rose quickly through the horticultural ranks in Britain, obtaining a horticultural diploma from the RHS in 1933, and in 1935 he became assistant to the director at Wisley. WWII saw him balancing military duties and assisting with national vegetable-growing schemes. Recruited from Wisley to run Washington Park Arboretum, the Mulligans arrived in Seattle in late 1946. He was hired as superintendent but within five months was promoted to director. He officially retired in 1972.

Book  (2003)  Page(s) 28.  
 
Rosa mulliganii Boulenger

Article (magazine)  (2001)  Page(s) 393.  
 
R. mulligamii Bouleng Ploidy 2x
Pollen fertility 42.2%
Selfed Fruit set 0%

Magazine  (2001)  Page(s) 22. Vol 95, Part 1.  
 
Peter Harkness.  Favourite Singles.
Rosa mulliganii Species climber, in UK 1917.   If garden space permits, a pergola where its dainty pendant clusters of saucer-shaped milk white flowers can display themselves and waft their scent around will, just after midsummer, provide an experience which will stay as a cherished memory ever afterwards for all who are fortunate enough to witness it.  This item may also be catalogued as Rosa longicuspis.

Book  (1997)  Page(s) 252.  Includes photo(s).
 
R. mulliganii ... Similar in many respects to R. rubus... Flowers single in small spaced clusters, pure white and scented... Many of the plants grown and sold as R. longicuspis) over recent years are actually this species)...

Book  (1996)  Page(s) 76.  Includes photo(s).
 
R. mulliganii Wild climbing rose. Hundreds of pendant stems laden with clusters of white flowers create an unforgettable picture of beauty as you view a pergola planted with this rose [and the photo Harkness provides supports that]... no one seems very sure of the true identity of the rose offered by growers under this name, seed of which was sent from Yunnan to the RHS Gardens at Wisley in 1919. Plants supplied as R. longicuspis are often found to be the same. The identity of Bryan Mulligan is surer; he was the Assistant to the Director at Wisley. The botanist to whom he sent the specimens to be indentified named the rose after him.

Book  (1995)  Page(s) 133, 146.  
 
[At Sissinghurst Castle] in the white garden the central arbour of Rosa mulliganii dominates the planting scheme at the beginning of July, while white 'Iceberg' roses are set in frames of box to formalize the arrangements...
p. 146: Rosa mulliganii (formerly known as R. longicuspis)...[this is incorrect taxonomically but may be a statement about confusion in commerce of the two species. Ed.]

Book  (1988)  Page(s) 38-39.  Includes photo(s).
 
Rosa mulliganii Boulenger. A rampant climber up to 6 m or more, with hooked prickles. Leaflets 5-7 glabrous above, dark shining green, the longest up to 6 cm long, glabrous above, pubescent on the nerves beneath. Flowers 4.5-5.5 cm across in a large loose corymb; pedicels 2.5-3.5 cm long, thinly pubescent and with numerous stalked glands. Sepals attenuate, 1.2-1.8 cm long. Hips 11-13 mm long. Close to R. rubus but with more leaflets, 5 or 7, not 3-5, longer pedicels and larger flowers, or R. brunonii but with glabrous shining leaves. This rose appears frequently in cultivation but is not recognized in Chinese floras. It was described from plants growing at Wisley, probably collected by Forrest in Yunnan.