Minute to medium-sized evergreen herbs. Stem creeping, apex upright. Leaves numerous; petiolar sheath with long marcescent ligule; blade elliptic, elliptic-oblong, linear-oblanceolate to obovate, coriaceous, punctate below, apex with tubular mucro; primary lateral veins pinnate, running into distinct marginal vein, higher order venation parallel-pinnate. Inflorescence solitary; peduncle subequal to petiole at anthesis, elongating later. Spathe ellipsoid, cuspidate, not constricted, lower part light green, convolute, broadly funnel-shaped, persistent, later subtending enclosing developing fruits, upper part white, gaping at anthesis, caducous immediately afterwards. Spadix sessile, shorter than spathe, with a few pistillodes at extreme base, female zone cylindric, narrower than upper parts, with pistils in 2-6 spirals; pistil depressed-globose, 1-locular, ovules many, orthotropous, attenuate towards micropyle, funicle distinct, placenta basal, stigma sessile, discoid, slightly concave in centre, narrower than ovary; sterile interstice a few rows (usually 2) of flattened, smooth, scale-like staminodes; male zone with 2-5 rows of stamens; stamens not grouped into flowers; filament distinct but short, flattened, connective ± inconspicuous, thecae ellipsoid, extrorse, dehiscing by pore at tip of conspicuous apical horn; pollen extruded in a droplet, inaperturate, ellipsoid, medium-sized (range 28-30 mm long (Grayum, 1992: 21), exine psilate; terminal appendix globose or ellipsoid to subcylindric, composed of truncate, obpyramidal to subcylindric, apically papillose staminodes, the uppermost ± connate. Fruit a globose to ellipsoid berry with numerous seeds; seed narrow-ellipsoid, with long, curved micropylar appendage, testa very slightly longitudinally ribbed to scabrous; embryo straight, elongate; endosperm copious.
HABIT : small evergreen herbs, stem creeping, apex upright. LEAVES : numerous. PETIOLE : sheath with long marcescent ligule. BLADE : elliptic, elliptic-oblong, linear-oblanceolate to obovate, coriaceous, punctate below, apex with tubular mucro; primary lateral veins pinnate, running into distinct marginal vein, higher order venation parallel-pinnate. INFLORESCENCE : solitary. PEDUNCLE : subequal to petiole at anthesis, elongating later. SPATHE : ellipsoid, cuspidate, not constricted, lower part light green, convolute, broadly funnel-shaped, persistent, enclosing developing fruits, upper part white, gaping at anthesis, caducous immediately afterwards. SPADIX : shorter than spathe, with a few sterile flowers at extreme base, female zone cylindric, narrower than upper parts, with gynoecia in 2-6 spirals, separated from male zone by a few rows (mostly 2) of flattened, smooth, scale-like staminodes, male zone with 2-5 rows of flowers, terminal sterile zone globose or ellipsoid to subcylindric, composed of truncate, obpyramidal to subcylindric, apically papillose sterile male flowers, the uppermost ± connate. FLOWERS : unisexual, perigone absent. MALE FLOWER : 1-androus, filament distinct but short, flattened, connective ± inconspicuous, thecae ellipsoid, extrorse, dehiscing by pore at tip of conspicuous apical horn. POLLEN : extruded in a droplet, inaperturate, ellipsoid, medium-sized (mean 29 µm., range 28-30 x 20-24 µm.), exine smooth (psilate). FEMALE FLOWER : gynoecium depressed-globose, 1-locular, ovules many, orthotropous, attenuate towards micropyle, funicle distinct, placenta basal, stigma sessile, discoid, slightly concave in centre, narrower than ovary. BERRY : globose to ellipsoid with numerous seeds. SEED : narrow-ellipsoid, with long, curved micropylar appendage, testa very slightly longitudinally ribbed to scabrous, embryo straight, elongate, endosperm copious.
Minute to rather large evergreen, obligate (very seldom facultative) rheophytic herbs. Stem creeping and rooting, with active apex upright, or erect, or stems rooted at base with remainder pendent and active tips ascending. Leaves mostly numerous; petiole shorter, equalling, or longer than leaf blade, often with conspicuous longitudinal ridges; petiolar sheath with a long marcescent ligule; blade elliptic, elliptic-oblong, linear-oblanceolate or obovate, stiffly coriaceous to membranous, often punctate abaxially, rarely so adaxially, apex mostly with a tubular mucro; primary lateral veins pinnate, adaxially flush with blade to prominently raised, abaxially ± flush with blade, running into variously distinct marginal vein; interprimary veins parallel-pinnate; higher order venation either parallel-pinnate or reticulate, or tessellate, usually very faint. Inflorescence solitary, or a few in sequence with each separated by a conspicuous prophyll or less often a foliage leaf; peduncle sub-equalling to much-exceeding petiole at anthesis, rarely (Bucephalandra gigantea) much shorter, always elongating later, often longitudinally keeled. Spathe ellipsoid to lanceolate, cuspidate, not constricted; lower spathe broadly funnel-form at and post-anthesis, persistent into fruiting, later subtending and enclosing developing fruits, light green to yellow or reddish, convolute; limb white, pink, or yellow, gaping at pistillate anthesis, variously senescing and then caducous at onset or during staminate anthesis. Spadix sessile or very briefly stipitate, shorter than spathe, usually with a few pistillodes at extreme base; pistillate zone cylindric to obconic, mostly narrower than upper parts, with pistils in 2 - 8 spirals; pistils mainly depressed globose or depressed trapezoidal, 1-locular; ovules many, orthotropous, attenuate toward micropyle, funicle distinct, placenta basal; stigma sessile, discoid, umbonate to slightly concave in centre, narrower than ovary; sterile interstice a few rows (usually 2, sometimes as many as 5 or as few as 1) of flattened, smooth, scale-like motile staminodes, these erect at pistillate anthesis, deflexing prior to staminate anthesis to seal lower spathe, turning green and persisting into fruiting; staminate zone with 2 - 9 rows of stamens; flowers unistaminate; filament usually distinct but very short, flattened, connective either inconspicuous or most often expanded as an extension of filament into a flattened triangular-cordate or spathulate structure with thecae on ventral surface of distal arms; thecae ellipsoid to globose, extrorse, dehiscing by a pore at tip of a short to long conspicuous apical horn; pollen extruded in a droplet, inaperturate, ellipsoid, medium-sized (range 28 - 30 µm long; Grayum 1992: 21), exine psilate. Appendix globose or ellipsoid to (sub-)cylindric, or bullet-shaped, composed of columnar to obpyramidal irregular polygonal to rounded apically papillose, echinate, smooth, or brain-like staminodes, uppermost often ± connate, less often appendix entirely comprised of connate staminodes. Fruit a globose to ellipsoid berry with numerous seeds, protected until maturity by persistent interstice staminodes; seed narrow-ellipsoid, with long, curved micropylar appendage, testa very slightly longitudinally ribbed to scabrous; embryo straight, elongate; endosperm copious.
Minute to medium sized evergreen rheophytes; petiole sheath with long marcescent ligule; leaf blade simple, elliptic to linear-oblanceolate, apex with tubular mucro, fine venation parallel-pinnate; spathe persistent in lower half, upper part caducous; spadix with terminal appendix of staminodes; thecae horned; stigma smaller than ovary. Differs from Phymatarum in unconstricted spathe, flattened sterile flowers between male and female flowers and smooth or verrucose male flowers.
The role of the interstice staminodes of Bucephalandra.
As noted above, Bucephalandra species are unique among Araceae by the presence of motile scale- or shield-shaped staminodes situated at the interstice of the pistillate and staminate flower zones. It has been speculated that these staminodes play a role in manipulating pollinators during anthesis by controlling access to the pistillate flower zone (Bogner 1980; Bogner & Hay 2000), but conclusive observations have been wanting.
Field observations of seven different Bucephalandra species (of which one is figured here for illustrative purposes) has established that pistillate anthesis begins 2 - 3 hours after dawn, with the spathe inflating to create a slit in the upper part of the spathe limb (Fig. 25B), the papillate stigmatic surface becoming sticky, producing a stigmatic droplet at pistillate anthesis, and production of a weak to rather powerful esteric or fruity odour attracting almost exclusively Colocasiomyia (Diptera: Drosophilidae), although recently B. aurantiitheca has been observed to be pollinated by a single species of Chrysomelidae (Coleoptera) (Fig. 2B). Pistil receptivity is c. 6 hours, and during this time the interstice staminodes and thecae are erect (Fig. 25C). The spathe limb remains in this "gaping" phase for c. 24 hours, but the interstice staminodes begin to lower by the evening of the same day (Fig. 25D, E). By midnight of the same day the tips of the lowered staminodes are pressed on the inner wall of the lower spathe, effectively sealing the lower spathe chamber (Fig. 25D, E). By this time the stigmas are dry and no longer receptive and the inflorescence is in the transition phase from pistillate to staminate anthesis. At no time do the interstice staminodes retain insects in the lower (pistillate) part of the spathe, and by the time they are sealing the lower spathe no insects are present in or on the inflorescence.
Staminate anthesis begins 2 - 3 hours after dawn on the second day. The staminate flower thecae reflex (Fig. 25E), and a second floral odour emission attracts a new wave of Colocasiomyia flies. Soon after this the spathe limb gape increases, and then very rapidly (less than 5 minutes) the limb abscises at its junction with the lower spathe (Fig. 25A), with the limb variously splitting and coiling outward from the margin. These rapid spathe limb movements coincide with pollen droplet extrusion from the tips of the thecae horns (Fig 25D & E). Staminate anthesis lasts c. 1 hour, at the end of which period all pollen droplets have been taken by the flies, and the spathe limb has fallen to leave the funnel-form lower spathe. Dependent on the species, between a few hours and four days after staminate anthesis the spent parts of the spadix above the interstice staminodes are shed to leave a faintly umbonate scar in the middle of a disk of white staminodes (Fig. 25F).
Within a few days of staminate anthesis, and provided fertilization has been successful, the staminodes sealing the persistent lower spathe change from white to green (apparently become photosynthetic), thicken, and harden (Fig. 25G). Most species also have tannin cells visible on the upper surface of the staminode. The staminodes remain in this condition until the fruits are fully developed, by which time the enlarged berries push the staminodes upward (Fig. 25H). Shortly after this, the staminodes become much paler and are then shed. This coincides with the now exposed fruits changing from green to yellowish green or yellowish white and rapidly decomposing to a mucilaginous pulp, in which are embedded the green seeds (Fig. 25I).
Dispersal is via a splash-cup mechanism, with water drops striking the inside of the erect persistent funnel-form lower spathe and ejecting the seeds. The seeds, with the aid of the micropylar appendage anchor on the mosses or tiny fissures on the surrounding rock. In summary, by the time that the interstice staminodes begin to lower, the pistillate flowers are already pollinated and/or the stigmas are no longer receptive. In all observations, interstice staminodes have no function in retaining pollinators inside the spathe during the anthesis transition period, as occurs in numerous unisexual-flowered aroid genera. Rather pollinating insects are attracted in two waves by separate floral odour emissions coinciding with the onset of pistillate and staminate anthesis. The appearance and texture of the post-anthesis staminodes, and their persistence until the mature fruit force their loss, is strongly suggestive of a role protecting the developing fruits. In many respects the interstice staminodes of Bucephalandra homeotically fill the role of the sloughing stylar plates of the monsterocarp of many Monsteroideae (e.g. Epipremnum Schott, Scindapsus Schott, etc.). The observations offered here are part of a wider and ongoing study of the biology of Bucephalandra. The results from that work are in progress.