Bentham's Cornel Vs. Kousa in PA
I had never heard of Bentham's Cornel (or evergreen Dogwood, as it is also known). By scrutinizing the pictures on the taxa pages of iNaturalist, I thought perhaps I could ID Bentham's by the bulbous fruit. Most of the Kousa's I am familiar with have a similar, odd, alien fruit, but I had never seen such bulbous proportions. Now am not sure that's such a good identifying characteristic.
One good identifying factor would be whether it is evergreen or not. Bentham's is evergreen, and Kousa is deciduous. However, there are now two Kousa cultivars that are also evergreen - "Empress of China" and "First Choice"... so that confounds that - not that it would be helpful in a photo situation anyways, where you do not track the tree through the seasons.
Zone could possibly be used to weed out Bentham's, as it only grows in zones 7-10. But there are some areas - particularly the southeast of PA - that are considered zone 7, and these areas may expand as our climate warms.
This is compounded by the fact that it hybridizes with Cornus Kousa - perhaps the above evergreen cultivars of Kousa were created from such a hybridization?
I suppose yet another question would be why does it matter. They both are non-native, but don't seem to be terribly invasive either. They both have similar properties in a garden. No one is likely to do research on either here in Pennsylvania... the only thing I am driven by is precision and desire to get to a species level in my identifications. This is something that comes up frequently on the identification page, and I'd like to definitively come to a conclusion.
The best source I've found so far on Bentham's Cornell
https://www.arthurleej.com/p-o-m-June04.html
Oregon State University seems to be a great resource for pictures of specimens of many plants including Cornus Kousa and Cornus Capitata. It looks like there are substantial differences in leaves and fruits.
https://oregonstate.edu/dept/ldplants/1plants.htm#cocap
I wish I could copy pictures into the body but it doesn't look like I can easily.
Here are their descriptions:
Bentham's cornel (Note they say it's hardy to zone 8 - other sources say that it has done well in zone 7)
•Evergreen tree/shrub, may reach 50 ft (15 m) when grown as a tree, but often smaller (20-30 ft; 6-9 m); may have similar width; horizontal branches. Bark brown or blackish gray. Leaves evergreen, simple, opposite, 5-12 cm, variable, ovate to lanceolate, leathery to thin, dark green above, gray-green below with dense appressed pubescence; turn red or purplish in fall. True flowers white, small, and in small terminal heads, surrounded by 4-6 large, 2-4 × 4-8 cm, rich cream color to pale yellow bracts, occasionally white, appear in summer. Fruit fleshy, rounded to strawberry-like, 2.5 cm across, green then crimson, reportedly edible, sweet; can be a litter problem.
•Sun to light shade. Unless grown from cuttings, trees don't flower until 8 to 10 years old (Sunset Western Garden Book, 2001).
•Hardy to USDA Zone 8 Native to evergreen and mixed forests, 1,000-3,200 m elevation; China (Guizhou, Sichuan, Xizang, Yunnan), Bhutan, India, Myanmar, and Nepal.
•capitata: growing in a dense head, presumably a reference to the true flower cluster.
Cornus kousa Cornaceae
Kousa Dogwood, Oriental Dogwood KOR-nus KOO-sa
•Deciduous tree/shrub, 15-18 ft (4.5-5.5 m), vase-shaped in youth, strong horizontal lines with age, exfoliating gray, tan and brown bark. Leaves simple, 5-10 cm long, opposite, have a drawn out tip, hair in axils of veins, dark green in summer, purplish-red or scarlet in fall. Flower buds at end of stems, fattened and globose, two bud scales form sharp point. "Flowers" are creamy-white, taper-pointed bracts (4, each 2.5-5 cm), the true flowers are small and make up the central sphere of the bloom. The blooms appear after the foliage emerges, usually a few weeks after the start of flowering of C. florida. Fruit (drupe) are initially green but ripen to pink or red, are spherical (13-25 mm diam.), on a 5 cm pendulous stalk (late Aug.-Oct.), they are edible but bland, with a mealy texture. (Some of our avian friends apparently disagree with this assessment, for they quickly eat the fruit after it ripens.)
•Sun to light shade, needs acidic, well-drained soil. More drought resistant and possibly less disease susceptible than C. florida (Dirr, 1998, p. 261).
•Hardy to USDA Zone (4) 5 Native to Japan, China, Korea.
•Many cultivars, over 80 (see Dirr, 2009, for an extensive list), including a few having pink-red floral bracts, e.g., ‘Radiant Rose’, and others with variegated leaves.
•cornus: the Latin name for Cornus mas. kousa: the Japanese name.
•Oregon State Univ. campus: north side of the Valley Library, in raised beds.
To me - the differences are the following:
Kousa leaf - thin, wide, coming to a very sharp point
Bentham's leaf - looks thick and dark green, oval, not coming to a sharp point, with a smooth slightly textured interior, like a button on a couch cushion.
Kousa flower - leaves more separated from each other pointing out in all four directions like a star, bracts sharply pointed, center having distinct "lumps" - not so smooth a look.
Bentham's flower - rounded bracts that overlap more and bunch forward in a rose-like appearance.
Fruit seems to be what is predominately recorded, often with fruits separated from the tree so no other means of identification is available. But this seems to be the least reliable way of identifying the species
Kousa fruit - slightly smaller than Bentham's, less bulbous, more uniformly red
Bentham's fruit - larger, more bulbous with a "Stretched" look, center calyx of each fruit a whitish color. However unripe fruits are small and can bear a close resemblance to immature kousa fruits.
I still think here in PA it is more likely to be a Kousa than Bentham's, but the best way to identify between the two is the leaf and flower.
