Factores influyentes en el análisis de tráfico de datos

The petiole in most rattan palms is somewhat variable in length (Dransfield, 1992a). It is usually much longer in juvenile individuals than in mature leaves and it may be absent altogether. The petiole, where present, and the rachis are often heavily armed with spines and it has been speculated are not necessarily adapted for the climbing process but appear to function as a means o f trapping litter from the forest canopy (Comer, 1966; Dransfield, 1992a). In taxa that lack petioles, the lowermost leaflets are also suggested to function as litter traps. The primary purpose of such trapping is assumed to be associated with the accumulation of nutrients {ibid.)

In the genus Laccosperma, some species (particularly L. secundiflorum) are characterised by a long petiole, whilst other species have a very short petiole {L. robustum and L. acutiflorum). In the species of Oncocalamus, the petiole is absent or much reduced, particularly in mature stems, although more conspicuous in the juvenile stage.

For many of the species of Eremospatha, the petiole is absent and the lowermost leaflets are modified such that they are much reduced and strongly reflexed so that they are swept back and clasp the stem. This clasping can be rather lax, or extremely tight, enclosing the stem completely. This enclosure is often colonised by ants (see C hapter 4).

1,2.13 Leaflets

The rattan leaf is pinnate (Uhl and Dransfield, 1987; Dransfield, 1992a). The leaflets result from the splitting of the folded leaf blade which occurs as the leaf expands. In almost all species of rattan, the leaflets consist of a single-fold; however, within some species of African rattan (L. secundiflorum and Oncocalamus wrightianus), leaflets can be composed of two or more folds.

Although, in general, the leaflets within the Calamoideae are entire, some taxa possess jagged, distal margins; these are termed praemorse. This character is particularly

common within the genus Eremospatha.

The leaflets of the majority of species of African rattan are linear. However, some species of Laccosperma, in particular, are sigmoid. Other leaflet shapes exhibited by the African rattans include the distinctive rhomboid leaflets of Eremospatha

wendlandiana and the more rounded rhomboid leaflets of E. cabrae and E. hookeri.

The manner in which the leaflets are held on the rachis is often highly diagnostic. In particular, the leaflets of Laccosperma robustum are conspicuously pendulous differentiating this species from other, closely related species of the same genus. The leaflets of Eremospatha macrocarpa are also somewhat pendulous distinguishing this species from other species within the genus. In addition, although the majority of the African rattan taxa possess leaflets that are arranged uniformly and singly on the rachis, the leaflets of Calamus deërratus may be grouped, particularly on the distal portion of the leaf. The slender forest species, Eremospatha quinquecostulata has characteristically clustered (or plumose) leaflets, arranged in groups of 4-6.

The presence of spines on the leaflet margins is a common feature of the African rattans and, where present, their size and arrangement is a good field characteristic for

distinguishing species. Laccosperma laeve, for example is devoid o f leaflet spines, and character is a useful means of distinguishing this species from the closely-related L. opacum. Accordingly, the long, fine, hair-like leaflet margin spines of L. robustum are a useful means of distinguishing this species from L. secundiflorum and L.

acutiflorum, which both possess rather short and robust spines on the leaflet margin.

In the majority of the African rattan taxa, the emerging leaf is a mid-deep green. However, Oncocalamus is often characterised by the presence of an orange or crimson expanding leaf, this turning deep green as it develops.

1,2,14 Climbing organs

Calamoid palms climb with the aid of two main organs; they may either have a flagellum or posses a cirrus. Flagella only occur in certain species o f Calamus, including C. deërratus, the sole representative of Calamus in Africa. The flagellum arises directly from the sheath and is regarded as a modified inflorescence (Fisher and Dransfield, 1977; Dransfield, 1978; Baker et a i, 1999d). Indeed, inflorescences of C deërratus are flagellate.

The remaining taxa within the Calamoideae, particularly those o f Asian origin, climb with the aid of a cirrus, a whip-like extension at the distal end of the leaf rachis armed with short, recurved thorns that often resemble a cat’s claw (Tomlinson, 1990). However, the three rattan genera endemic to Africa, Laccosperma, Eremospatha and Oncocalamus, possess a vegetative morphology unique within the Calamoideae and the cirrus is actually a marked extension between the distal leaflets. The leaflets are present as reduced, reflexed thorn-like organs termed acanthophylls. This structure is also present in some members of the unrelated genera present only in the New World; Chamaedorea (sub-family Ceroxyloxideae; tribe Hyophorbeae) and Desmoncus (sub­ family Arecoideae; tribe Cocoeae). These taxa also climb through the means of reflexed terminal leaflets. Coincidentally, many species of Desmoncus are also exploited for their cane-like qualities and are used in the same way as the true rattans (Henderson and Chavez, 1993).

Figure 3. A canthophylls o f Laccosperma acutiflorum, Campo, C am eroon (Sunderland 1926)

On the low er portion o f the stem s o f som e taxa in the genera E rem ospatha and

O ncocalam us, an undifferentiated rachis is often produced, devoid o f any true leaflets

and possessing acanthophylls only. This unusual, and previously unrecorded, organ seem s to be m ore com m on on younger stem s, particularly under a forest canopy.

H ow ever, this organ also occurs in O ncocalam us colonising recently cleared areas as

well. The adaptive significance o f this organ is not know n, although it certainly facilitates the establishm ent o f the developing stem s and assists in the clim bing process. In the absence o f an existing term for this appendage, I have applied the term “elam inate” (devoid o f le a f blades) to signify the lack o f true leaflets on the rachis.

1.2.15 Floyvering behaviour

In all, 16 genera o f palm s, the m ajority o f them in the C alam oideae, produce w hat appears to be a m assive “term inal” inflorescence that results in the death o f the

prim ary axis o f the palm . In fact, this structure is not term inal (Corner, 1966) but is an aggregate inflorescence that consists o f a large num ber o f lateral inflorescence units borne in the axils o f the leaves, w hich are often reduced. These inflorescence units are borne in the distal portion o f the stem and m ature sim ultaneously (Tuley, 1965; Uhl

and D ransfield, 1987, T om linson, 1990). T his condition is term ed hapaxanthy. In essence, there is no m orphological difference betw een the inflorescences in hapaxanthy and pleonanthy, its opposite condition. O f the three endem ic A frican

rattan genera, Laccosperm a is hapaxanthic, w hilst Erem ospatha and O ncocalam us are

pleonanthic. C alam us deërratus is also pleonanthic. See C h a p te r 5 for further elaboration o f hapaxanthy and pleonanthy in the A frican rattans.

Figure 4. Elam inate rachis o f O ncocalam us tuleyi. Southern Bakundu FR, C am eroon (Sunderland

1761)

1.2.16 The inflorescence and floral morphology

Fisher and D ransfield (1977) show ed that adnation o f the inflorescence to the internode or the lea f sheath occurs in several rattan genera. In the C alam inae, the inflorescence is adnate to the internode and the sheath above its axil o f origin such that the inflorescence appears to arise from the sheath itse lf (B aker et al., 1999d). The flagellum o f C alam us deërratus, being a m odified inflorescence, is attached in this way. The other rattan genera in A frica do not display any inflorescence adnation (although fid e B aker et a l , 1999d).

In common with other members of the genus, Calamus deërratus possesses dyads of unisexual flowers, however the inflorescence units of the endemic rattan genera of Africa also somewhat unique within the Calamoideae. The genera Eremospatha and Laccosperma are composed of dyads of hermaphroditic flow ers\ Although the dyad composed of unisexual flowers is itself a common feature within the Calamoideae, the dyad composed of hermaphroditic flowers is unique within the Palmae and is

considered to be an unspecialised form of flower arrangement (Uhl and Dransfield, 1987; Baker ûr/., 1999b; 1999d). '

In contrast, the flower cluster of Oncocalamus is distinctive and complex, not only within the Calamoideae, but in the Palmae as a v^holQ.^'pmœalamus is monoecious, and consists of a central 1-3 pistillate flowers with two lateral cincinni subtended by a single bract, with each cincinnus bearing basal 1-3 pistillate flowers and 3-5 distal staminate flowers.

F igu re 5. D iagram o f selected d yads w ithin the C alam oid eae sh ow in g a r r a n e ^ e n t s o f flow ers in h erm ap h rod itic, m onoecious and d ioeciou s taxa.

Laccosperma Ererrtspatha (Hermaphroditic) Oncocalamus (Monoecious) Calamus (Dioecious)

With the exception of the genus Eremospatha which, uniquely in the Palmae possess an inflorescence that is free of conspicuous bracts, the Calamoideae possess strictly tubular bracts that are rather uniform in shape (Baker et al., 1999d). As such, within the genera Laccosperma and Oncocalamus, as well as Calamus deërratus, the rachis bracts are tightly sheathing. In the former two genera, these bracts are often prone to splitting and tattering post-anthesis.