Leaf blades on magnolia floral buds

by John D. Freeman and floral buds are entirely enclosed and protected by a pair of leaf parts, Occasional development of a leaf the stipules, which may be much larger blade near the apex of a Magnolia in the case of floral buds than in either flower bud has probably been observed typical Magnolia leaves or vegetative by many who collect, study, and grow buds. Paired stipules are sometimes these plants. Discovery of an example apparently fused into one unit (as in of this anomaly on a branch of t)f. Magnolia) or may be present as macrophylla collected by Harold separate valve-like structures (as in Hopkins and me at Oak Hill, AL, in Liriodendron). Since the outermost May 1985 (see photographs) led to flower parts are enclosed by stipules in development of this note at his Magnolia buds, the outer perianth suggestion. segments are not primarily protective. The botanical nature of the When little distinction exists among structure(s) enclosing Magnolia buds, perianth segments except the relative both vegetative and floral, is somewhat positions, they are typically called unusual. In most plants the scales tepals rather than sepals and petals. covering vegetative buds represent Abscission scars from stipules produce leaves that are reduced in size and the rings that encircle young twigs in specialized to protect bud contents, but members of Magnoliaceae. If one not in Magnolia. The outer portions of tends to think of bud scales of floral buds in most species consist of Magnolia in terms of function instead perianth segments (actual flower parts) of origin, this can lead to the erroneous known as sepals, but not in Magnolia. assumption that they are In the Magnoliaceae both vegetative morphologically equivalent to the

These photos show the position of the leaf growth appendage on the M. macrophylla flower bud. ln left photo the leaf growth arises from the flower bud, which is partly hidden at top br the leaf growth at this camera angle. In right photo, from the other side of the flower bud, the poim of leaf auachment is hidden from the camera and the leaf arises from behind the flower bud. while a normal growing shoor with a new leaf appears at the left below the 4ower peduncle. This budded branchlet was cut and inserted in a container of water for several days, but the bud, though it appears mature, dried up and the Jlower never opened, leaving a question of whether the leaf growth normally would have fallen away with the spathaceous bracr surrounding the bud or remained on the tree. l9 protective scales covering buds of other given species of plant before first plants. making observations. Vegetative leaves that have a blade, a The form attained by leaves as they petiole, and stipules, like those of differentiate within buds is under the Magnolia, are termed romplere leaves. control of many factors operating in If one (or more) of these three types of concert. These factors include several foliar parts should be lacking, that leaf plant hormones that must interact is described as incomplete. Incomplete with the environment to develop a leaves thus may be elaminate (without plant's genetic potential. Abnormal a blade), epetiolate or sessile (without leaves represent products of various the petiole), or estipulate (lacking the malfunctions in this complex growth pair of stipules). Normal bud sheaths control system. Certain anomalies may of Magnolia are elaminate, epetiolate show up annually in certain individuals leaves that develop during formation of or appear for one season in a plant and winter buds. Except in very rare cases never be seen again. It is probable that the blades and petioles of such the growth potential of the primordial specialized leaves simply do not cells that might form leaf blades can be develop. However, just as normal altered by the environment as well as leaves usually have axillary buds, the the genes themselves. For example, leaf stipular sheath of a Magnolia flower blades may develop on Magnolia has an axillary bud that later can flower buds more commonly following lengthen the stem from just below a mild winter than an extremely cold where a terminal flower had been one because undifferentiated blade formed. tissue is more likely to be killed by the Very little experimental work has low temperatures and drying in the been done with stipules, but their latter case. Pitcher-leaved Magnolia absence or presence has been useful in specimens (Maouomx, vol. XIX, No. I, descriptive botany. Among flowering pp. 15-16, and No. 2, p. I9) are plants in general. presence of stipules another phenomenon attributable to is regarded as a primitive feature. They flaws in the system controlling leaf occur in many different forms among development, and in this case the diverse plant groups, some of which atypical form appears to have a genetic are considered on other grounds to be basis. Indeed, the balance between relatively advanced, Most members of genetics and environment has the rose and bean families have numerous manifestations in the genus conspicuous stipules. The thorns of Magnolia. black locust (Robinia), for example, are stipules. In Begonia, a common houseplant representing its own family, they are large and membranous. In the greenbrier (Smilax) stipules take the form of tendrils, whereas in cinnamon fern (Osmunda) they are flattened, non-green extensions of each leaf base near the juncture of petiole (stipe) and rhizome. The word "stipe, " used for the petiole of ferns, is the source of the term stipule, meaning a small appendage of the leafbase. Stipules usually occur in pairs at the bases of These leaves of M. officinalis turned leaves, but sometimes they are tubular ro a golden color and remained on the and surround the stem as in smartweed iree for awhile before falling. Sir Perer (PolJgonunt). It is best not to predict Smirhers rhoughr the effect was the form that stipules may assume in a anranive, and sent this pirrure. 20