Latin name of genus and species:Physocarpus opulifolius.

Variety denomination: ‘ZLENora’.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinct cultivar ofPhysocarpus opulifoliusand will be referred to hereafter by its cultivar name, ‘ZLENora’.Physocarpus opulifolius(commonly known as ninebark, common ninebark, Atlantic ninebark, and Eastern ninebark) is a deciduous shrub grown for landscape use. The key objective within thePhysocarpus opulifoliusbreeding program I initiated in St. Paul, Minn. in 2001 and now continue in River Falls, Wisc. has been to develop newPhysocarpus opulifoliuscultivars that are compact growing, well-branched, healthy, and possess colorful foliage. One specific goal has been to produce a yellow-green leaved cultivar similar toPhysocarpus opulifolius‘Dart's Gold’ (not patented) but possessing more resistance to powdery mildew and having a more symmetric and full plant habit. ‘ZLENora’ meets this goal.

‘ZLENora’ originated as a unique seedling within an F2population that was developed by open-pollination of twelve F1seedlings (growing in isolation) of the cross ofPhysocarpus opulifolius‘Donna May’ (disclosed in U.S. Plant Pat. No. 22,634) as the female parent andPhysocarpus opulifolius‘Dart's Gold’ (not patented) as the male parent. Ninebark displays self-incompatibility, and it is expected that the seeds that developed were from crosses between compatible full siblings. Seeds were harvested and bulked together from the F1siblings. Pollination that led to this F2population of seedlings from which ‘ZLENora’ was identified occurred in June 2014. The seeds of this population germinated during the winter of 2014/2015 indoors under florescent lights in St. Paul, Minn. ‘ZLENora’ stood out early on as a young seedling for having the brightest yellow-green foliage of all the new seedlings that season. After danger of frost was past, it was transitioned outdoors where it continued to be grown in a container. It was first asexually propagated using softwood cuttings its first summer (summer 2015). I have found that the characteristics of ‘ZLENora’ are stable and true to type over successive generations of vegetative propagation.

‘ZLENora’ is unique relative to other ninebark seedlings in my breeding program and all cultivars I am aware of because of its relatively bright yellow-green foliage, relatively strong powdery mildew resistance, and moderate overall plant and leaf size with improved plant density and symmetry for yellow-green leaved cultivars of similar overall plant size. ‘ZLENora’ first flowered in 2017. It has attractive blush-white flowers that are abundant and attractive against the colorful foliage. As follicles develop in full sun, they are a light coral-pink color for about a month and provide additional ornamental value. Vigorous current-season stems can naturally branch to a slight to moderate degree without pruning. The propensity for current season stems to branch leads to a naturally fuller and more symmetric plant habit than other moderate to larger sized cultivars on the market which typically possess stronger apical dominance and no to very limited current season branching without pruning.

SUMMARY OF THE INVENTION

The primary objective of the breeding goal was substantially achieved, along with other desirable improvements, as evidenced by the following unique combination of characteristics that are outstanding in the new variety and that distinguish it from other ninebark in my breeding program, as well as from all other cultivars ofPhysocarpus opulifoliusof which I am aware:1. Upright, mounded, moderately dense plant habit;2. Moderate overall plant size;3. Moderate branching characteristics;4. Medium sized yellow-green foliage;5. Short to moderate internode length;6. Resistance to powdery mildew;7. Corymbs of blush-white flowers;8. Light coral-pink follicle color in full sun for about a month after fertilization;9. Ability to root and grow vigorously from softwood and semi-hardwood stem cuttings.

Asexual reproduction of this new cultivar by rooting of softwood and semi-hardwood cuttings, as performed at River Falls, Wisc. and Cottage Grove, Minn. shows that the foregoing and all other characteristics and distinctions come true to form and are established and transmitted through succeeding asexual propagations.

Comparison with Parents

‘ZLENora’ was a seedling in the F2generation from a cross of ‘Donna May’ and ‘Dart's Gold’. Compared to ‘Dart's Gold’ the plant habit of ‘ZLENora’ is a bit more dense and symmetrical without pruning and ‘ZLENora’ has displayed greater resistance to powdery mildew. ‘ZLENora’ and ‘Dart's Gold’ have similar foliage color and foliage size. Compared to ‘Donna May’, ‘ZLENora’ has an overall larger plant and foliage size. ‘Donna May’ has purple foliage, while ‘ZLENora’ has yellow-green foliage.

Comparison of ‘ZLENora’ with Similar Cultivars

ThePhysocarpus opulifoliuscultivars with the greatest similarity to ‘ZLENora’ are ‘Dart's Gold’ and ‘Podaras 3’ (disclosed in U.S. Plant Pat. No. 22,362). Overall plant size and foliage color and size are similar between ‘ZLENora’ and ‘Dart's Gold’, but ‘ZLENora’ is slightly more dense and well-branched and has greater resistance to powdery mildew than ‘Dart's Gold’. ‘ZLENora’ and ‘Podaras 3’ have similar resistance to powdery mildew and foliage size and color, but ‘ZLENora’ is more compact growing and well-branched than ‘Podaras 3’.

