Monographs Details: Lagenocarpus rigidus (Kunth) Nees
Authority: Maguire, Bassett. 1965. The Botany of the Guayana Highland. Mem. New York Bot. Gard. 12 (3): 1-285.
Discussion:This species belongs to a taxonomically most difficult complex including L, rigidus, L. tremulus, L. tenuifolius and their m a n y close allies. The complex can easily be defined by the large compound fasciculate panicle with pendant staminate partial inflorescences, fuscous sheaths, and oval to obovoid fructifications. that are more or less foveolate or rugose and conspicuously constricted at the base of a short conical beak. The distribution range of the complex covers the West Indies, the Guayana Highland and the southeastern part of Brazil from Bahia southwestewards to Sao Paulo. L. guianensis resembles this complex in general features but is distinct from it by the erect, rigid staminate branches and quite smooth fructifications without any conspicuous constrictions between the body and the long beak.
Due to the great variability in both vegetative and floral parts, a number of names have been published at both specific and infra-specific levels within the L. rigidus complex, but actual differences among these taxa have never been investigated satisfactorily. C. B. Clarke based his new taxa largely on dimensions of various parts of plants. Similarly H . Pfeiffer, w h o studied the entire genus monographically, differentiated taxa by the density, size and the manner of branching of inflorescence and in some instances by the size of fructifications. In order to testify to the reality of these taxa, which are after all based on qualitative characters, variations have been investigated on 171 specimens selected at random from major United States herbaria including F, NY and US. As a result, in this complex the size and features of fructifications were found to have very little taxonomic significance for separation of taxa, as fructifications vary from 2.5 to 4.5 mm in length, elliptic to obovate or broadly obovate in shape, and from conspicuously foveolate or rugose to almost smooth in texture (Fig. 8, A - F ) . There is no discontinuity in any of these characters. The structure and form of inflorescence provides no criteria for taxonomic distinction. The inflorescences' show continuous variation from a narrow, loose panicle to a large compound panicle consisting of several partial fascicles; the form often correlated with vigor and size of plants.
Variations in leaf characters have also been checked in the 171 specimens mentioned above. A s seen in Table 2, measurements of leaf width show a bimodal concentration, and there L. tenuifolius, circumscribed by the narrow leaves less than 5 mm wide, can be separated from the rest of the plants of this complex having broader leaves more than 5 m m wide. No morphological character was found to divide the narrow-leaved L. tenuifolius any further.
The plants of the L. rigidus-tremulus alliance have broad leaves more than 5 mm in width. L. tremulus originally described from British (juiana differs slightly from L. rigidus of southeastern Brazil by leaf differences. In L. tremulus leaf blades are generally septate-nodose at least toward the base and are never curled though sometimes in dry localities, weakly recurved, whereas in L. rigidus they are not septate-nodose and radical blades are strongly to moderately curled. So far as we have examined specimens, all plants from the West Indies faU under the category of L. tremulus, while all specimens from southeastern Brazil show the feature of L. rigidus. The plants from the Guayana Highland, however, are a mixture of L. tremulus, L. rigidus and intermediate forms between these two plants. Furthermore the intermediates show two different character combinations of leaves, i.e., septate and curled leaves, and non-septate and non-curled blades.
For a better understanding of the relationship between L. tremulus and L. rigidus, 110 specimens selected at random from the Guayana collections of The New York Botanical Garden have been divided into four groups in accordance with four different character combinations of leaves, and the number of specimens of each group has been tabulated in Table 3. In this table remarkable correlations have been detected in the two character combinations representing the phenotypes of typical L. tremidus and L. rigidus respectively. Although we do not intend to go any further on this problem without experimental work, the segregation ratio of the four phenotypes of Table 3 suggests a linkage in leaf character and possible hybridization between L. tremulus and L. rigidus in Guayana. From this consideration and the geographical distribution of the two assumed parents, L. rigidus and L. tronulus, L. tremulus is recognizable in Guayana though not clear-cut. All the other broad leaved specimens, representing binomials that were proposed chiefly by H. Pfeiffer (1922) and Gilly, are included within the variation range of the complex discussed above.
Very variable L. rigidus is thus regarded as consisting of three subspecies: rigidus, tenuifolius and tremulus.