Hoya pubicalyx

Identification

Hoya pubicalyx is a climbing shrub, hairless except for its flower clusters, with stems about 3 mm thick and internodes up to 20 cm long ^[1]. E.D. Merrill’s 1918 description gives fleshy leaves, pale and glossy, oblong to oblong-obovate, 10–14 cm long and 3–5 cm wide, with a blunt base and a distinctly pointed tip. About six pairs of lateral veins run up from the midrib but are hard to see. The petiole is about 1 cm long ^[1]. NC State describes the foliage as long, narrow, thick and glossy, deep green and sometimes marked with silver specks ^[3].

The flower clusters are large: many-flowered and 8–9 cm across, with slender spreading pedicels about 3.5 cm long ^[1]. Each flower is about 1.8 cm across. The corolla lobes are broadly triangular and densely papillate inside, and the corona is a star 10–12 mm wide with glossy, pointed lobes ^[1]. The name refers to the calyx, which is hairy on the outside, as are the pedicels ^{[1, 3]}.

Look-alike. Hoya carnosa has shorter, broadly ovate to elliptic leaves with a rounded or slightly heart-shaped base ^[5]. H. pubicalyx leaves are longer and taper to a distinct point ^[1].

Naming and trade labels

The accepted name is Hoya pubicalyx Merr., described in 1918 from a specimen collected at Mauban in the former Tayabas Province, Luzon, now Quezon ^{[6, 1, 2]}. WCVP lists no synonyms for it ^[6].

Watch for misspellings on labels and in databases. ASPCA lists the plant as “Hoya publcalyx” under the common name silver pink vine ^[4]. Two cultivar names appear on NC State’s page: ‘Splash’, with green leaves speckled white and pink, and ‘Silver Pink’, shown as a hanging-basket plant ^[3].

Growing it

NC State publishes care guidance written for this species.

• Light. Give bright, indirect light, ideally about six hours of filtered sun a day. Direct sun should be limited to no more than two morning hours, because it can scorch the leaves ^[3]. NC State explains that strong sun turns the leaves reddish, as anthocyanin pigments act as a sunscreen for young growth, and that mature leaves can take on a silver-pink tone in good light ^[3]. See the light guide.
• Water. Water often during the growing season, letting the mix dry out between waterings, and water less in autumn and winter. NC State suggests filtered water or rainwater, and warns that too much water leads to root rot and leaf drop ^[3]. See the watering guide and root rot.
• Humidity and temperature. NC State recommends 60–70% relative humidity and says to keep the plant above 50°F (10°C), since it does not tolerate frost and cooler air damages the foliage ^[3]. See the humidity guide.
• Pot and support. Use a pot with good drainage, such as terracotta. The plant does not mind tight roots, so repotting is rarely needed. Give it a vertical support to climb ^[3]. See trellising.
• Pests. NC State names mealybugs, aphids and whiteflies ^[3]. See hoya pests.

In the wild, the type plant grew on trees along streams in damp forest ^[1]. Co’s Digital Flora adds records from forest near the seashore, at 0–152 m ^[2].

Flowering

NC State describes H. pubicalyx as slow to mature and flower, taking up to two years. Blooms come in spring and summer and are most fragrant in the evening ^[3]. Merrill also recorded the flowers as fragrant ^[1].

The upper part of each flower stalk forms a thickened rachis about 4 mm across ^[1]. NC State advises against removing old blooms, because the same spur produces flowers for several years ^[3]. See hoya peduncles and why a hoya is not blooming.

Notes on sources

The only botanical description found is Merrill’s original one, which was written from dried specimens. It gives flower colors only as brown when dry ^[1]. The fresh pink color on this page comes from NC State ^[3].