Book  (2021)  Page(s) 60.  Includes photo(s).
 
Translation:
The flowers of ‘Alba Semiplena’ often have 11-22 petals, divided into 8-12 large, outer corolla petals and 3-10 small and often rolled or twisted petaloids in the centre of the flower. The flowering shoots can also produce slightly more blooms and the variety often forms more rose hips than ‘Alba Maxima’. The scent is medium to strong, clean, and fresh with hints of citrus and cherry peel.

Magazine  (Jun 2020)  Page(s) 18 vol 42, No. 2.  Includes photo(s).
 
R. alba semiplena photo Andrew Ross. 

Newsletter  (Feb 2016)  Page(s) 4.  
 
The other rose, situated at the bottom half of the engraving, is ‘Rosa Alba Multiplex’. In Prevost’s catalogue of 1829, it is called ‘Rosa Alba Maxima Multiplex’. Like the previous rose, this one goes by several names, including ‘Alba Maxima’, ‘Alba Flore Pleno’, ‘Angelica Alba’, and the ‘Jacobite Rose’. Technically R. x alba maxima, it also appears as ‘Alba maxima multiplex’ in manuals and catalogues of 1817 (Audibert), 1833 (Keller), 1836 (Boitard) and 1838 (Gore). A tall, lovely specimen grows in the old rose garden of Sacramento’s Historic Cemetery
[The engraving is more like Alba semi-plena]

Article (magazine)  (2013)  Page(s) 76-80.  
 
...Rosa alba L. also known as the white oil-bearing rose has been cultivated in relatively small areas in Bulgaria during the last century, together with R.damascena. There are no clear historical records on the time of introduction and the origin of the white oil-bearing rose in Bulgaria, but it is considered that the initiation of industrial cultivation of R.alba has probably happened together with R.damascena. The Institute of Roses, Essential and Medical Cultures (IREMC) in Kazanlak, Bulgaria, which is the main supplier of essential oil rose planting material in the country possesses a rich collection of R.alba accessions collected during the last quarter of the 20th century from different rose plantations in the Rose Valley. The oil-bearing R. alba possesses some agricultural advantages over R. damascena, like elevated tolerance to diseases and unfavorable climatic conditions. The composition of essential oil distilled from the flowers of R. alba available in IREMC’s rose collection has already been determined and has been demonstrated to be very similar to that of R. damascena (Nedkov et al., 2009; Dobreva and Kovacheva, 2010; Dobreva and Gerdzhikova, 2013). Since the rose oil distilled from R. alba flowers possesses similar composition to that of R.damascena, in Bulgaria the flowers of R. alba have been traditionally mixed and distilled together with that of R. damascena. However, the flowers of R. alba possess a lower content of rose oil compared to that of R. damascena (Dobreva and Kovacheva, 2010; Kovacheva et al., 2011). This is the main reason the rose growers to cultivate this oil-bearing rose species in small areas in Bulgaria, currently accounting for around 600–1000 decares...
PCA analysis was performed based on the flower biometric data for the 38 analyzed R. alba accessions from IREMC’s genetic resources collection. The obtained PCA plot revealed the existence of two distinct flower pheno groups (Fig.1). The majority of samples, including 31 accessions fell into the group PG:1 [Alba maxima]characterized by higher flower weight, smaller flower diameter, higher number of petals and lower number of anthers (Table1). The other seven accessions characterized by lower flower weight, bigger flower diameter, lower number of petals and higher number of anthers fell into the second group PG:2 [Alba semi-plena]....
As in the case of R. damascena (Rusanov et al., 2005), all analyzed R.alba accessions are clones and originate from a common ancestral genotype together with the well-known European garden rose varieties, R.alba Maxima and R. alba Semiplena. Despite the demonstrated common clonal origin of the analyzed R. alba accessions they differ in the flower phenotype and form two distinct flower phenogroups, PG:1 and PG:2, which fit well to  the flower phenotype of R.alba Maxima...and R. alba Semiplena....The micro-satellite analysis also suggests that the accessions possessing one of the observed flower phenotypes, or their clonal ancestors, have derived as a sport from the plants possessing the other phenotype, supporting the view of Thomas (1994) on the origin of R.alba Semiplena as a sport of R. alba Maxima.The genetic base of the observed two flower phenotypes is not clear and could involve changes of expression pattern or functionality of single or small number of genes due to single mutation, transposon jumping and/or epigenetic changes...
Phenogroup PG:1 
Flower weight (g) 3.64 +/- 0.54; Flower diameter (mm) 53 +/- 5; Number of petals 52 +/- 6; Number of anthers 41 +/- 10
Phenogroup PG:2
Flower weight (g) 2.35 +/- 0.30; Flower diameter (mm) 66 +/- 5; Number of petals 17 +/- 2; Number of anthers 91 +/- 11

Book  (2012)  Page(s) 31.  
 
Rosiers Blanc
Alba 1^re Série...
(R. Blanc semi d. Dupont
(- Semi-plena Godefroy
[synonyms]

Book  (Feb 2009)  Page(s) 21.  
 
‘Alba Semi-Plena’/R.alba suaveolens/R.alba nivea: Les rosiers Albas – blancs. Connu au moins depuis le XVIème siècle… Comme tous les Albas, ce rosier est très résistant au froid, et forme sans conteste, l’un des plus jolis arbustes à floraison blanche qu’il soit possible de planter dans un jardin. En Bulgarie, il est utilisé en haies pour entourer les champs de roses à parfum… NB: On distingue parfois cette rose – qui serait une mutation de ‘Alba maxima’ intervenue en 1867 – de R.alba suaveolens Dieck, en culture depuis le XVIè siècle. Mais, dans la mesure où il est de plus en plus communément admis que c’est, au contraire, ‘Alba Semi-Plena’, qui est, en fait, le type originel dont est issue ‘Alba Maxima’, la mutation de 1867 en constitue qu’un retour au type et il n’y a pas lieu de dissocier ces deux formes.

Article (magazine)  (2009)  Page(s) 30.  
 
'Alba semi-plena'   Source RJBM [Réal Jardin Botanico Madrid] Chromosome Number 42

Article (misc)  (2005)  Page(s) 111, Table 5-1.  
 
Alba Semi-Plena : Hexaploid

Book  (2002)  Page(s) 18.  
 
Rated 9.0

Magazine  (2002)  Page(s) 17. Vol 96, Part 1.  
 
Peter Harkness.  White Rose of York .....