Habit

The information on the habit of the species of Rhodostemonodaphne has for the most part been taken from herbarium labels.  The patchiness and unreliability of this information warns against overstating the significance of these data.  Notwithstanding, collection label data can be very informative when interpreted carefully with prior knowledge of the living plants.

All species of Rhodostemonodaphne are dioecious.  All fertile plants seen (live or dry) had flowers with only one set of functional sex organs.  Pistillate flowers sometimes have well developed stamens with large locelli, but I have never seen pollen within them.  Staminate flowers sometimes have rudimentary ovaries, but these lack a stigma and an ovule.  No indication of sex change is known.  Three trees collected twice with ca. one year intervals had pistillate flowers and fruits both times (BAFOG 361-M, 7425; Kröll-Saldaña 134, 326; Kurz B-9, B-28-14).

The majority of the species of Rhodostemonodaphne are medium to large trees 10-30 m tall and ca. 20 cm in diameter at the base.  The maximum recorded height is 45 m for an individual of R. kunthiana (although 15–30 m is more common for that species; one tree I collected was a canopy tree 30 m tall).  Seven other species are known to attain 30 m or more; these include R. elephantopus, which has the maximum recorded trunk diameter for the genus of 80 cm.  Buttresses ca. 70 cm tall and spanning ca. 30 cm from the trunk have been reported for some of these species.

The distinction between small trees and shrubs is obviously vague.  In designating a small individual as a tree or a shrub, I am guided by the terminology used by the collectors and the general appearance of the herbarium sample.  Lax, thin twigs are taken as suggestive of a shrubby habit.  The smaller tree species (i.e., ca. 10 m tall) such as Rhodostemonodaphne debilis, R. crenaticupula, R. frontinensis, R. laxa, and R. capixabensis may also be called shrubs.  A few species appear to be consistently shrubby; these are R. avilensis, R. curicuriariensis, R. licanioides, R. miranda, R. parvifolia, and R. steyermarkiana.  Among the shrubs, a very characteristic growth form is that of the scandent shrubs as illustrated by R. celiana and R. scandens. The scandent shrubs have thin, long, little-branched axes, and grow interwoven with or reclining on the neighboring vegetation.  These species grow on sandstone outcrops where the vegetation tends to be of low stature.  Putting together information available on habit, habitat, and guided by the morphology of the twigs, it seems likely that R. debilis, R. crenaticupula, R. curicuriariensis, R. licanioides (in one label described as having drooping branches), R. miranda, and R. tumucumaquensis, may also be scandent shrubs.  These, and the “true” scandent species all tend to have undulate to bullate leaves.  The scandent, shrubby habit of Endlicheriavinotincta C. K. Allen is remarkably similar to that of R. celiana, and both species grow on the sandstone formations of the Guayana highlands.  Other similarities in indument and inflorescences, and specially their similar glandular outgrowths on the stamens, call for a close relationship between these species (Rohwer et al., 1991).  Nevertheless, because of their differences in locelli number they are placed in different genera.  Rhodostemonodaphne steyermarkiana, a third species from the Guayana highlands, has similar leaf characteristics to R. celiana and R. scandens.  In label notes it is invariably described as a shrub, without mention of a scandent habit.  However, the branching dynamics of this species differs somewhat from that of the two scandent species in that the flushes produce lateral branches regularly, unlike the long unbranched flushes of R. celiana and E. vinotincta.

Even when available, the information on bark and wood characters provided by the collectors is very inconsistent in terms of the description of the surface sculpturing, outer and inner bark colors and thickness, wood odor and color.  I have nevertheless added it to the species descriptions when available.  The copious, clear mucilage exuding from the bark of Rhodostemonodaphne penduliflora is unique in the Lauraceae so far as I know.  An observation commonly made in field notes for R. kunthiana is that its wood characteristically oxidizes dark orange to black upon exposure.

Architecture

The architecture of Rhodostemonodaphne appears to conform to the models previously reported for other species of Lauraceae, i.e., Rauh’s, Attims’, Massart’s, and Roux’s models (Hallé et al., 1978).  Most species in the family have monopodial trunks with spiral (generally 2/5) phyllotaxy, continuous or rhythmic growth, and mostly orthotropic branches, these also with spiral phyllotaxy (opposite-leafed species are always present in small genera such as Anaueria, Aspidostemon, Caryodaphnopsis, Chlorocardium and Dahlgrenodendron, and are common in Cinnamomum, but are otherwise rare in the Lauraceae).  The branches can be secondarily plagiotropic as they become parallel to the ground with age.  Flowering does not influence the architecture of the plants.  A report of distichous leaf arrangement in the branches of an unidentified species of Cryptocarya from New Caledonia (Hallé, 1978, citing Veillon, 1976, unavailable to me) is very unusual and suspect (the same condition reported for Cassytha filiformis L. is probably due to the extreme morphology of this parasitic genus).

Although the Lauraceae are consistently monopodial, their shoot morphology is far from being monotonous.  In Rhodostemonodaphne, as well as elsewhere in the family, some species have a markedly rhythmic growth (e.g., R. anomala), while in others growth is more or less continuous with no apparent rest (e.g., R. avilensis), as evidenced by morphological indicators such as scale leaf scars, and/or short internodal regions.  A characteristic feature of R. rufovirgata is the production of whole flushes, with leaves, branches, and inflorescences, prior to the elongation and lignification of the main axis.

Differences in lateral branch position in the flushes of rhythmically growing plants, are important in characterizing species, groups of species or even genera (cf. Endlicheria subgenus Ampelodaphne, and Actinodaphne).  In Rhodostemonodaphne the majority of the species have basitonic branching, where the branches of a new flush are produced from the axils of cataphylls or basal foliage leaves.  The result is often pseudo-verticillate branching, as observed in R. laxa, R. leptoclada, R. scandens, and R. penduliflora.

Rhodostemonodaphne kunthiana has architecture and flushing dynamics that stands out from all others thus far known in the genus.  The growing axes do not show a marked resting period.  Nevertheless, there seems to be a certain periodicity in growth: zones along the main axis where lateral branches are produced are followed by zones with no lateral branches or inflorescences.  The branches thus tend to be arranged in pseudo-whorls.  These branches are for the most part more vigorous than the parent axis, resulting in a chandelier-like arrangement.

The terminal buds of Rhodostemonodaphne are always covered with cataphylls.  The cataphylls can be elongated and pointed, giving the bud a slender appearance, or thickened and blunt.  The cataphylls are mostly caducous, but sometimes, as in the case of R. licanioides,R. miranda, and R. scandens, they persist on the twigs through at least two growing seasons.

Indument

Most species in the genus have some type of indument, although nearly glabrous or soon glabrescent individuals are found in many species.  In the two species described as glabrous, R. longipetiolata and R. penduliflora, the buds at least have some type of hair covering.

The hairs in Rhodostemonodaphne, as in all Lauraceae, are invariably unicellular and simple.  They generally have a conspicuous lumen, but solid hairs are also present.  The indument may soon disappear, or persist through more than two growing seasons.  The buds and expanding leaves are mostly covered with appressed-ascending hairs.  The hairs can remain straight and appressed on the twigs and leaves, resulting in a sericeous indument, as in species of the R. grandis-complex, or become erect, or be straight to crisped.  Depending on the length and density of the hairs, the indument of twigs and leaves can be described as puberulous, tomentose, pubescent, or velutinous.  Indument terminology follows that proposed by Hewson (1988).  Hair coloring varies among the species, and even within a species, from translucent to whitish, yellowish, brownish, or reddish.

The indument provides  important characters in distinguishing species or even groups of species in Rhodostemonodaphne. In the R. grandis-complex, all species have a characteristic sericeous indument, consisting of long, straight, appressed, yellowish to brownish hairs, giving a silver to golden appearance.  This indument can nevertheless be caducous and noticeable only on young plant parts.  In other cases, however, indument type can be variable within a species, or even within an individual.

Rhodostemonodaphne kunthiana is remarkable in terms of the variation of indument types present.  As is discussed in detail in the species discussion, indument of R. kunthiana can vary from a covering of short and crisped, to long and curved to straight hairs.  Although the former are generally associated with plants collected in lowland forests, and the latter with collections from montane forests, this pattern of variation is not clear cut (differences in indument types observed within an individual may also correspond to different growth stages of the plant).  Hair color here also varies from light yellow to reddish-brown.

Rhodostemonodaphne dioica is unusual in that the indument on the underside of the leaves consists of two types of hairs, erect and appressed.  Another comparable case, where the indument is mixed, is Nectandra reticulata and some of its allies (J. G. Rohwer, pers. comm.).  On the twigs, however, the indument of R. dioica consists only of long, straight to curved, erect hairs.

Leaves

The leaves of Rhodostemonodaphne are spirally arranged in a 2/5 phyllotactic pattern.  Sub-opposite or pseudo-verticillate leaves, as found elsewhere in Lauraceae (e.g., Endlicheria subgen. Ampelodaphne, Actinodaphne, etc.), are not normally observed, although some specimens of R. scandens tend to have pseudo-verticillate leaves at the end of the flushes.

The petioles can be robust (nearly as thick as the twig they are borne on) or slender, and terete to adaxially flattened to nearly canaliculate.  Some species have what I refer to as a “pulvinate” petiole.  This consists of a short, thickened, terete petiole and is found characteristically in Rhodostemonodaphne miranda.  Pulvinate petioles are often found in species with a shrubby habit and in plants growing on white sands or sandstones.

Leaf blade consistency can vary greatly within species and even individuals.  A tendency to have an undulate or distinctly bullate lamina is common in some species, but in all species where a bullate lamina has been observed, flat laminae are also present.  The lamina is usually elliptic, and it varies in size from less than 10 cm in length, as constantly found in Rhodostemonodaphne avilensis or R. parvifolia, to up to 40 cm long as in R. penduliflora.  Abnormally large leaves, as often found in sterile collections, are most likely taken from stump sprouts or saplings.  The base of the lamina can be distinctly rounded to acute or cuneate.  A conspicuously cordate base, rare in the family as a whole, is found in the only known collection of R. miranda; minutely cordate bases are also found in some specimens of R. licanioides.  Apices are rounded to acute, and are most often mucronate to acuminate.  The leaf margin is mostly flat along its length, but in some species it is recurved at the base.  Rhodostemonodaphne revolutifolia is distinctive in that the leaf margins of the mature leaves are strongly revolute along their entire length; R. recurva generally has leaves with recurved margin near the base.  A few collections of R. macrocalyx from the southern extreme of its range have unusually lobed leaves.

The venation is mostly eucamptodromous, the secondary veins looping near the margin, but fading before connecting with the next secondary vein.  Towards the leaf apex the secondary veins tend to be more strongly connected than elsewhere.  Only Rhodostemonodaphne scandens and R. licanioides are strictly brochidodromous, with all the secondary veins connected near the margin.  In some species there is a slight tendency towards an acrodromous venation, where the basal-most secondary veins are stronger than the rest.  In a number of species some of the secondary veins bifurcate in mid-lamina.  In a few species the tertiary veins are distinctly scalariform, running perpendicular to the secondary veins (e.g., R. kunthiana), but in most species they are random-reticulate.

Inflorescences

The inflorescences are mostly located towards the base of the flushes, but mesotonic or acrotonic inflorescences, as well as those found along the whole length of the flush, also occur. In the majority of the species, the inflorescences are erect. Pendulous inflorescences (e.g., Rhodostemonodaphne penduliflora, as observed in the living specimen) are also present in the genus, although these may be under-reported. As a rule the inflorescences have a determinate axis and cymose second order branches. The number of second order branches and the degree of branching varies both between and within species. The staminate inflorescences usually have higher orders of branching than the pistillate ones. Second order branches are mostly scattered along the main axis, but in a few species they are clustered apically (e.g., R. morii, R sordida). Inflorescences vary from ?gspicoid?h thyrses, with no more than three branch orders (i.e., the main axis plus constricted lateral simple cymes, e.g., R. miranda), to lax, thyrsoid inflorescences with up to eight branch orders (e.g., R. macrocalyx). Bracts and bracteoles are mostly caducous, but in some species (e.g., R. revolutifolia) they are persistent. In general, the inflorescences have the same type of indument as the twigs.

Flowers

On the basis of their external morphology, staminate and pistillate flowers are indistinguishable.  The flowers usually have a conspicuous pedicel, although nearly sessile flowers are found in R. scandens and R. miranda.  The pedicel is usually of equal width throughout, but in a number of species it is trumpet-shaped and gradually merges with the receptacle (e.g., R. laxa).  The receptacles themselves are mostly distinct from the pedicel and obconical, although in a few species they are almost non-existent, while in others they are well-developed, globose, and often constricted at the place of tepal inception.  The indument of the pedicels and receptacle as well as that of the abaxial surface of the tepals is mostly similar to that of the twigs, although it is generally shorter.

The general arrangement of flower parts is typical of the Lauraceae tribe Perseeae (see Figure 1).  There are two alternating whorls of tepals, nine stamens in three alternating whorls (labeled I, II, and III, from without inwards; in a few species a fourth, staminodial whorl [IV] is present), and a unicarpellate pistil.  The tepals of the two whorls are equal to sub-equal in size.  At anthesis they are mostly broad, and spreading or recurved; small, distinctly erect tepals are characteristic of R. morii alone.  A number of species have light colored tepals, ranging from green to cream to white, but yellow, salmon or distinctly red tepals are not uncommon.  The adaxial surface of the tepals is glabrous, hairy, or (in R. penduliflora) papillose.

Variation in stamen morphology is extensive and comparable to that observed in the vegetative organs.  As with most Lauraceae, the stamens of Rhodostemonodaphne of whorls I and II are similar, and very different from those of whorl III.  In most species the anthers of the outer two whorls are thickened and sessile, with four locelli arranged in an arch towards the apex.  Filiform stamens are characteristic of R. macrocalyx; stipitate, laminar anthers are found in R. capixabensis; and the strap-like (loriform) stamens of R. synandra are unique to that species.  Rhodostemonodaphne recurva, R. cyclops, R. morii, and R. penduliflora vary in locelli number, while in R. revolutifolia, the only known staminate individual has in the outer whorl two-locellate anthers, and those of the only known pistillate individual have four vestigial locelli.  In the four-locellate species, the medial locelli are always introrse, while the two exmedial ones can be introrse, or in R. kunthiana, approaching a latrorse position.  Most species have glabrous anthers, but sometimes with a few hairs at the base; those of R. kunthiana and allies are hairy, while R. penduliflora is unique in having distinctly papillose anthers.  The stamens of whorl III are mostly columnar, with a pair of glands at the base, and have four locelli; in most species the lower locelli are extrorse, while the upper ones are either extrorse or latrorse.  Only in R. penduliflora is there a reduction of locelli number to two and in some cases one; furthermore, these locelli are introrse (note however, that the only known specimen of R. penduliflora is pistillate).  The size, shape, and degree of fusion of the glands at the base of the stamens of whorl III varies greatly.  Two species, R. peneia and R. praeclara, consistently lack glands on whorl III, while in the flowers of R. longipetiolata with doubled whorls (see discussion under R. longipetiolata), they were also absent.  Two species, R. celiana and R. penduliflora, have paired glands at the base of the stamens of whorls I and II, these, however, are not distinct and globular as are those commonly found at the base of the anthers of whorl III. Glands in whorls I and II are otherwise very rare in the Lauraceae and their presence in these species needs to be confirmed.  Staminodia of whorl IV are generally absent, except in three species, R. celiana, R. elephantopus and R. miranda, where they are sometimes present.

In pistillate flowers, the locelli of the staminodia of all whorls vary from fully developed to completely lacking.  In all cases where the locelli were opened there was no pollen.  The pistil in staminate flowers is sometimes fully developed but lacks an ovule; more often it is reduced to a filiform appendage or is completely absent.  When present, it is often obscured by the partially fused stamens of whorl III.  In pistillate flowers the ovary is ovoid or globose, and is either enclosed by the receptacle, or is borne on top of it surrounded only by the staminodes of whorl III.

Pollen

In a contribution to the pollen morphology of Neotropical Lauraceae (Raj & van der Werff, 1988), two species of Rhodostemonodaphne were studied (R. grandis and R. kunthiana).  The pollen grains of these species are apolar, spheroidal, 21–24 µm in diam., and inaperturate.  The exine is 0.5–1 µm thick, and covered with monomorphic vestigial spinules, scattered 1–2 µm apart.  The spinules in both species are plain, lacking the usual twisted strands observed in other closely related genera (e.g., Ocotea, Nectandra, and Pleurothyrium).

Fruits

The pedicels in fruit vary from evenly thickened to gradually enlarged, forming a trumpet-shaped cupule, with the exception of Rhodostemonodaphne juruensis with a spreading disk-like cupule and R. antioquiensis with a reflexed cupule.  When dry the cupules are commonly coriaceous and have a smooth surface.  Normally the margin is undulate and the tepals persist in fruit as cupular appendages.  The cupules of species in the R. grandis-complex and those of R. kunthiana differ from the rest in that they are distinctly pedicellate, woody when dry, warty or lenticellate (in R. kunthiana and R. synandra), and have a straight margin.  The single?]seeded berries are nondescript and elliptic to ovoid.  The great majority of the field notes report the ripe fruits as having a red cupule and blackish berry, as is common for most Lauraceae.  The fruits of the species of Rhodostemonodaphne for which these are known are shown in Figures 2–3.