Always rewarding is to find a shrub that produces showy flowers during the cool winter months. For that role, yellow flax, Reinwardtia indica Dumortier (family Linaceae), certainly deserves mention from our collection. If you are walking along the stream, you will find our specimen of this weak-stemmed shrub growing along the western path. During most months of the year yellow flax is hardly noticed, because it has unremarkable elliptic, very thin-bladed leaves, dull green above and pale green beneath, but midday in December or January you may witness as many as two dozen yellow flowers that are open. Each golden-yellow flower, 5 cm wide, lasts that one day and is described as being fugacious, meaning that the corolla withers and falls off easily.
Reinwardtia is a genus of only two species that are native to southern and southeastern Asia, R. indica and R. sinensis. It commemorates Caspar Georg Carl Reinwardt (1773-1854), a Prussian-born Dutch botanist who held important positions and professorships in The Netherlands but also served as the founder and first director of agriculture of the botanic garden at Bogor (Buitenzorg) in Java, then a Dutch colony. Reinwardt certainly was a key figure of his time, because in addition to the Belgian Dumortier three other authors independently published the eponymic genus Reinwardtia for plants of three different families. Rules of botanical nomenclature permit only one, the earliest legitimately published genus name, to stand.
Our specimen is an evergreen shrub 1.5 meters in height with very thin stems, which bend very easily without breaking. This is also a characteristic of its blue-flowered cousin, commercial flax (Linum usitatissimum), the stems of which can easily be tied into knots. The soft, tough fibers of flax used to make linen are produced on the outer cover of the stems (in the phloem), and Reinwardtia likewise has these fibers. When its stems die and that fibrous cover is shed, the woody skeleton is very brittle and easily broken. This must be why the plant never attains significant height, although our plant is substantially taller than described in the literature.
New shoots are produced with the alternate leaves. Using a good hand lens you should be able to see a pair of tiny, brownish stipules at the petiole base for each new leaf, but these are quickly shed without leaving much evidence that they were ever there. The thin blades, produced on a petiole up to one centimeter in length, exhibit entire margins but sometimes also very shallowly toothed margin toward the tip. The blade ends in an abrupt point (it is mucronate).
Flowers of R. indica are produced on rather short shoots from each axillary bud. On that axillary shoot form several tiny leaves (or bracts) that are nearly colorless except being green at their tips, followed by a 1-cm stalk (pedicle) bearing the flower. Most of the flowers on the shrub are solitary in this manner, but at the shoot tip they appear to be more clustered and cymelike where leaves do not expand. The erect flower bud is covered with five overlapping pale green, lance-shaped sepals, and emerging from them is the prominent, tubular, funnelform corolla, broader (5 cm) than it is long.
Looking face on, the corolla is composed of five petals fused to form the 2-cm tube. The corolla's golden-yellow color is improved by the presence of fine reddish veins; such lines are termed nectar guides or nectar lines, because they typically communicate to pollinating insects where to go to find a nectar reward. The five corolla lobes are cleverly overlapped (imbricate). Emerging from the floral tube are observed three curiously shaped green stigmas on three styles nearly two centimeters in length. You must dissect the flower under magnification to observe that the styles are fused above the small, superior ovary. Five yellow stamens form a ring around the ovary and tend to be about half the length of the pistil, and alternating with stamens you may be able to observe the colorless, sterile teeth, called staminodes.
Our plant never seems to form fruits. Fruits of Reinwardtia are described in the literature as being globe-shaped capsules, each with three or four chambers (locules), two seeds per locule, and breaking apart at maturity into six or eight segments. In frost-free climates, where cultivated plants form fruits, R. indica has become escaped. But we, apparently, are not so lucky.
ARTHUR C. GIBSON, MEMBG Director