University of Richmond UR Scholarship Repository

Biology Faculty Publications Biology

Summer 2012 Closely Paired Flowers Produce Single Fruit W. John Hayden University of Richmond, [email protected]

Follow this and additional works at: http://scholarship.richmond.edu/biology-faculty-publications Part of the Botany Commons, and the Plant Biology Commons

Recommended Citation Hayden, W. John. "Closely Paired Flowers Produce Single Fruit." Bulletin of the Virginia Native Plant Society 31, no. 3 (Summer 2012): 5, 8.

This Article is brought to you for free and open access by the Biology at UR Scholarship Repository. It has been accepted for inclusion in Biology Faculty Publications by an authorized administrator of UR Scholarship Repository. For more information, please contact [email protected]. Bulletin of the Virginia Native Plant Society Partridge berry Closely paired flowers produce single fruit Perhaps one of the most striking production in cymes can continue by This illustrates, I hope, the power features of partridge berry (Mitchella successive repetition of pairs of later of a comparative perspective to make repens), the 2012 VNPS Wildflower of flowers forming below earlier flowers. sense of plant form. All the intermedi- the Year, is its closely paired flowers Cymes are widespread in Rubiaceae, ate stages may not be known in that yield a single berry fruit (figure the family in which partridge berry is Rubiaceae, but given a simple three- 1). That these fruits are double struc- classified. It should be easy, therefore, flowered cyme as a hypothetical start- tures, formed by pairs of flowers, is to interpret the paired flowers of par- ing point and tightly paired flowers tridge berry (figure 3) as a simple cyme with fused ovaries and fruits as an end- in which the terminal flower is absent point, similar intermediate stages to and the rare instances of three-flowered those seen in Caprifoliaceae may be in- clusters (figure 2) as a typical, simple, ferred to have occurred in the ancestry cyme. Further, the flowers are tightly Figure 1 of Mitchella. paired simply because their individual Viewed from another perspective, revealed in the presence of two dis- pedicels (flower stalks) are very short. partridge berry represents the small crete rings of five sepals each on the A parallel situation exists in the hon- end of the scale in terms of floral aggre- fruit apex, or in some cases, by a single eysuckle family, gation in Rubiaceae. Consider, for ex- ring of 10 sepals. Viewed in isolation, Caprifoliaceae. ample, buttonbush (Cephalanthus without context, the nature of these Like Rubiaceae, occidentalis), in which hundreds of double fruits may seem perplexing, this family has flowers are tightly gathered into a glo- but as in so many things, a compara- cyme-based inflo- bose head-like inflorescence, which can tive perspective helps to make sense rescences, and two- be interpreted as the condensation prod- of conundrums such as this one. flowered cymes with uct of an extremely large compound First, let’s consider the paired oc- terminal flowers absent cyme consisting of many flowers. In currence of flowers. While two-by-two are common. Examples buttonbush, unlike partridge berry, the is the usual configuration, examina- include the flowers are merely close, not really tion of many partridge berry plants in twin-flower fused together; in fact, each floret is flower will reveal occasional excep- (Linnaea bo- separated from its neighbors by several tions. As pointed out by Blaser (1954), realis, so beloved Figure 3 minute bracts. Other globe-headed instances in which three flowers are by Linnaeus that he named the plant for Rubiaceae with crowded but separate produced (figure 2) are significant, as himself), beauty bush (Kolkwitzia flowers are known, for example the are instances in which amabilis), and honeysuckles (Lonicera Asian genus Adina, sometimes culti- anatomical/micro- species). The paired flowers of honey- vated as an ornamental. scopic remnants suckles are particularly interesting in Finally, we should consider of a third flower that a series of species show progres- Morinda, another globe-headed genus of can be found be- sive degrees of fusion between the ova- Rubiaceae, but one in which the densely tween the two ries of paired flowers (Wilkinson 1948): crowded ovaries do fuse together, à la well-developed the American fly-honeysuckle (L. those of Mitchella. There are about 80 flowers. These ob- canadensis) has essentially no fusion of species of Morinda found throughout the servations sug- paired ovaries, various species shows tropics including M. royoc, a vine-like gest that, funda- intermediate degrees of fusion, while the shrub or small tree that extends from the mentally, par- paired ovaries of sweet-breath-of-spring Caribbean into southern Florida and M. tridge berry (L. fragrantissima) can be fused for citrifolia, the noni fruit, originally native Figure 2 produces flowers nearly their entire length but still re- to tropical Asia but now cultivated in a pattern known as a cyme, or di- tain, as in partridge berry, two distinct throughout warm regions. M. chasium. Cymes constitute one of the remnants of calyx (sepals) at the apex yucatanensis (figure 5)—a plant that I fundamental inflorescence patterns (figure 4). The double fruits of know from the forests of Yucatan, found in flowering plants; a cyme is partridge berry Mexico—and for which the general re- characterized by one flower that ter- and sweet- semblance to partridge berry should be minates a stem and a pair of flowers breath-of- obvious is illustrated on page 8. In the that diverge from opposite sides of the spring appear much larger flower clusters of Morinda, stem at the node directly below the ter- to be morpho- however, flowering is sequential, rather minal flower; typically, the terminal logically than simultaneous as in partridge berry. flower opens first, followed by the two equivalent Nevertheless, each component ovary of lateral flowers. Potentially, flower Figure 4 structures. (See Similar behavior, page 8) Summer 2012 Page 5 Bulletin of the Virginia Native Plant Society •Similar behavior (Continued from page 5) Figure 5 Morinda retains its individual calyx and all the fruits are thoroughly fused together, just like partridge berry, but in Morinda, a dozen or more flowers, rather than just two, are fused together. In fact, the fruit of Morinda, like mul- All illustrations by berries and pineapples, is a good ex- Nicky Staunton ample of what is known botanically as a multiple fruit. berries and their paired double fruits And here is another example of the are not so odd, not so idiosyncratic, benefits of a comparative perspective. after all—at least they are no stranger The double berries of Mitchella are sel- than pineapples. The two fused ova- dom described as multiple fruits, but ries of partridge berry that form a single clearly, that is what they are. Funda- common fruit is merely the simplest mentally, it matters not that only two possible example (n=2) of a multiple fruits derived from two flowers are fruit. A comparative perspective per- fused together; fused fruits from closely mits one to see perplexing structures spaced flowers define the term. Never- for what they really are. theless, it may seem a stretch to assert References that little partridge berries are in some •Blaser, J. L. 1954. The morphology of the fashion morphologically equivalent to flower and inflorescence of Mitchella much larger examples of multiple fruits repens. American Journal of Botany 41: like mulberries and pineapples. Com- 533-539. •Wilkinson, A. M. 1948. Floral anatomy paring partridge berry with Morinda, and morphology of some species of the however, should remove any doubt; the tribe Lonicereae of Carpifoliaceae. Ameri- only real difference between the two is can Journal of Botany 35: 261-271. the number of flowers/fruits that are John Hayden, VNPS Botany Chair ultimately fused together. So, partridge