Pinguicula ramosa — Vorstman's Guide to the Carnivorous Plants

Identification

A small rosette of leaves eight to fifteen millimetres long and five to eight wide, with rounded tips and inrolled margins, often half sunk in moss. The species character is the scape: fifteen to ninety millimetres long and forked into two or three branches, each carrying a flower — unique in the genus and visible from a distance. The flower is white, seven to eleven millimetres long, with a two-lobed upper lip and a lower lip whose lobes are unequal; the spur is short, conical and yellow, one and a half to four millimetres. Flowering is June and July. Out of season the plant withdraws into a small winter bud among the moss.

Similar species

In flower confusion is impossible: no other butterwort branches its scape. Out of flower the rosette could pass for a young Pinguicula macroceras, which grows in the same Japanese mountains, but that species becomes far larger — leaves up to fifty-five millimetres — and has a blue-purple flower on an unbranched scape. P. vulgaris does not occur in Japan. The habitat is also very particular: a dry, sheltered, vertical rock face under an overhang, in shade. A small butterwort found there in Nikko is almost certainly this species.

The trap and how it works

A flypaper trap in a setting unusually dry for this genus. The rock faces the species grows on lie under overhangs and receive hardly any direct rain; moisture comes from high humidity and from water seeping through the rock. That makes the droplet on the stalked glands a costly item the plant must be sparing with. The sessile glands release digestive enzymes only once prey is lying on the leaf; the margin then rolls inwards. The catch consists of springtails, gnats and other small insects living in the moss and in the crevices of the wall. On bare volcanic rock, with no soil and so no mineral nutrition, that catch is virtually the only source of nitrogen.

Habitat and ecology

Vertical, moss-covered volcanic rock faces at fifteen hundred to seventeen hundred metres, usually north-facing and half to deeply shaded (R1), in the forest belt and along wood edges and gorges (B5). Overhanging portions protect the faces from direct rainfall, giving the mosses and the plant a stable microclimate. Companions include Saxifraga fortunei and Primula modesta, both typical plants of damp Japanese rock walls. The climate is cool, with deep snow in winter.

Distribution and elevation

Endemic to Japan and in practice confined to a few mountains in the Nikko district of Tochigi Prefecture, on Honshu. That makes it one of the smallest ranges in this book. The altitudinal band is narrow, between fifteen hundred and seventeen hundred metres, and the number of suitable rock faces within it is limited. The area lies largely inside a national park, but that does not protect the faces from every kind of pressure.

Recorded (one-degree cells)

Distribution based solely on records at GBIF (Global Biodiversity Information Facility), not on TDWG regions — those are often far larger than the actual range. The light halo is the area around a record, the dark core the record itself. The darker square is the only one-degree cell — roughly a hundred and ten kilometres — in which the species has been recorded, from all GBIF records. This is coarser than for most species because hardly any record of this plant carries an accurate coordinate. It shows where the species has been seen, not where it occurs: an empty square means nothing.

Forms and variation

No wild varieties are recognised. What varies is the number of branches on the scape — usually two, sometimes three — and the length of the spur, which runs from one and a half to four millimetres. Plants on deeply shaded faces stay smaller and paler than those in half shade. The branched scape itself is not an aberration but the species character: it occurs in all plants and is not sometimes present and sometimes not. No natural hybrids have been described; at this elevation no second butterwort shares the same faces.

Where and when to see it

This is a species to look at and not to touch. The Nikko faces are known, partly protected and sensitive to trampling; climbing on or beside these rocks damages the moss the plants root in. From the path, scan the shaded side of rock faces and under overhangs, and watch for the branched stalks with their white flowers in June and July — recognisable from several metres and far more conspicuous than the rosette. Binoculars are more use here than a lens.

Conservation status

The species has not been assessed for the global IUCN Red List and is not in CITES, so there is no international category. Nationally the picture differs: in Japan it counts as endangered and is strictly protected. The causes named are erosion and damage to the rock faces, partly by climbers, the effects of acid deposition on the moss carpet, and above all the sharply increased grazing pressure from deer, which on Mount Koshin has stripped the vegetation back to bare rock and brought the local population to an acute crisis. For a species with a handful of sites on one massif, that means the world population hangs on a few walls.

Scientific name

Pinguicula ramosa | Miyoshi ex Yatabe, 1890

Described by Manabu Miyoshi in 1890, in Botanical Magazine Tokyo 4: 315, based on material collected on 9 August 1890. The type locality lies on Mount Koshin-zan, in the former province of Shimotsuke (present-day Tochigi Prefecture), Japan, at a rock cliff called Fuji-sengen along the trail between the Koshin-sanso hut and the summit. The name "ramosa" (branched) refers to the flower stalk, which in this species — uniquely within the genus — is forked near its base. The Japanese name koshin-so ("Koshin plant") refers directly to the type locality, Mount Koshin-zan.

World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.