Hoya kerrii

Identification

Hoya kerrii is a hairless climber with very thick, fleshy leaves. In the original description, W.G. Craib gave the leaves as obovate to nearly round, 4–12 cm long and 5–9.5 cm wide, with rolled-under margins and a tip split into two rounded lobes ^[1]. That notch is what turns the leaf into the familiar “heart”, with the stalk attached at the point ^[4]. The lateral veins are not visible ^[2]. The petiole is short and thick, 5–15 mm long ^[1].

Leaf size varies a lot between accounts. Flora of China, which describes plants in cultivation in southern Guangdong, gives 4–6 × 5–6 cm ^[2], while NParks gives leaves 5–15 cm long ^[4].

The flowers come in globose clusters ^[3] 4–5 cm across, on a common peduncle 2–3 cm long ^{[1, 2]}. Craib measured each corolla at about 9 mm across with the lobes rolled back, whitish with a red-tinged center, and a thick, reddish corona ^[1]. NParks describes the corona as pinkish-brown to purplish-brown ^[4].

Look-alikes. Craib described H. kerrii as close to Hoya obovata but distinguished it by the two-lobed leaf tip and flowers nearly half the size ^[1]. In H. obovata the leaf tip is rounded and only rarely notched ^[8]. Hoya australis can also have near-round leaves, but they end in a short point rather than a notch and, in New South Wales plants, are densely hairy underneath ^[10].

Naming and trade labels

The accepted name is Hoya kerrii Craib, published in 1911 from material collected by A.F.G. Kerr in northern Thailand ^{[11, 1]}. Costantin later reduced it to a variety of H. obovata (H. obovata var. kerrii), and that name is now treated as a synonym ^{[11, 2]}. A 2022 checklist of Sulawesi hoyas notes that the relationship between H. obovata, H. kerrii and similar species has still not been studied ^[9].

Variegated plants are sold under cultivar names. NParks lists ‘Albomarginata’, with irregular cream leaf edges ^[5]. NC State lists ‘Variegata’, with a green leaf center and a creamy white border ^[6].

Many sweetheart hoyas are sold as a single rooted leaf in a pot, especially around Valentine’s Day. NC State warns that such a leaf is unlikely to grow into a plant unless some stem tissue was cut with it ^[6]. See water vs substrate propagation.

Growing it

NParks and NC State both give care notes written for this species.

• Light. Bright, indirect light; NParks lists it as a semi-shade plant ^[4]. See the light guide.
• Water. The plant does not tolerate waterlogging. NParks advises letting the mix stay slightly dry and watering potted plants when the top 3 cm has dried ^[4]. NC State reads thin, brown or wrinkled leaves as a sign the plant is drying too far between waterings, and warns that overwatering can hold back flowering ^[6]. See the watering guide.
• Warmth and humidity. NC State gives 65–80°F as the ideal range and says cooler conditions slow growth and flowering. It suggests a humid room such as a kitchen or bathroom ^[6]. None of the institutional sources consulted gives a minimum temperature for this species, so that field is left blank.
• Potting mix and pot. NParks suggests a slightly acidic to neutral mix of one-third orchid mix and two-thirds potting mix, and says the plant grows and flowers best when rootbound ^[4]. NC State links root rot to pots that are too large for the roots ^[6]. See the substrate guide.
• Feeding and growth. NParks recommends a light monthly feed of general fertilizer at half strength and describes growth as slow ^[4]. NC State advises against cutting back the long, bare twining stems, which come before new leaves and flowers ^[6].
• Pests. NParks mentions scale insects and mealybugs; NC State lists aphids, spider mites and mealybugs ^{[4, 6]}. See hoya pests.

ASPCA lists H. kerrii as non-toxic to dogs, cats and horses ^[7]. NParks, however, flags the sap as an irritant and lists the plant as toxic if eaten, without giving details ^[4].

Flowering

NC State notes that young plants can be slow to flower ^[6]. NParks describes the flowers as long-lasting and scented at night ^[4]. NC State adds that open flowers drip plenty of reddish-brown nectar that can stain fabric and furniture ^[6].

Leave the old flower stalks in place, because new buds form on them, and do not move the plant once buds have appeared ^[4]. If a mature plant will not bloom, see why a hoya is not blooming.