Monographs Details: Myrcia guianensis (Aubl.) DC.
Authority: Maguire, Bassett. 1969. The botany of the Guayana Highland-part VIII. Mem. New York Bot. Gard. 18: 1-290.
Family:Myrtaceae
Discussion:

Eugenia guianensis Aubl., PI. Guiane Fr. 506. pi. 201. 1775.

Myrtus pyrifolia J.-St. Hil. in Duham., Arb. ed. 2. 1: 208. 1800-1801.

Myrcia elegans D C , DC. Y'\odr.'.\: 251. 1828.

Myrcia exsurca D C , DC. Prodr. 3: 247. 1828.

Myrcia lauriflora BC, DC. Prodi, i: 252. 1828.

Myrcia spixiana D C , DC. Prodr. 3: 251. 1828.

M y m a ob/2<5a Schauer, Linnaea 21: 272. 1848.

Myrcia surinamensis Miq., Linnaea 22: 170. 1849.

Calyptromyrcia elegans (DC.)'R&rg,'Lmnd.t& 21: 34. 1855.

Calyptromyrcia spixiana (DC.) Berg, Linnaea 27: 35. 1855.

Aulomyrcia lauriflora (DC.) Berg, Linnaea 27: 64. 1855

Aulomurcia surinamensis (Miq) Berg, Linnaea 27. 64 .1855

Aulomyrcia dichroma Berg, Linnaea 27. 65. 1855

Aulomyrcia obtusa (Schauer) Berg, Linnaea 27.66.1855

Aulomyrcia obtusa p pauciflora Berg, LinnsLea. 27: 67. 1855.

Aulomyrcia obtusa y panicularis Berg, Linnaea 27: 67. 1855.

Aulomyrcia obtusa 5 tenuifolia Berg, Linnaea 27: 67. 1855.

Aidomyrcia obtusa e longipes Berg, Linnaea 27: 67. 1855.

Aidomyrcia roraimensis Berg, Linnaea 27: 68. 1855.

Aulomyrcia cuneata Berg, lAnnaea. 27: 72. 1855.

Aulomyrcia schomburgkiana Berg, Linna.ea. 27: 75. 1855.

?Aulomyrcia conduplicata Berg, hinnaea 27: 76. 1855

Aulomyrcia e.T5Mcca (DC) Berg, Linnaea 27: 79. 1855

.

Aulomyrcia pridnosa Berg, Mart. Fl. Bras. 14(1): 114. 1857.

Aulomyrcia poeppigiana Berg, Mart. Fl. Bras. 14(1): 123. 1857.

Aulomyrcia gard7teriana Berg, Mart. F\. Bras. 14(1): 129. 1857.

Aulomyrcia uaupensis Berg, Mart. Fl. Bras. 14(l): 518. 1858.

Aulomyrcia androsaemoides Berg, hinnaea SO: 661. 1861.

Aulomyrcia buxizans Berg, Linnaea 30: 664. 1861.

Myrcia roraimae Oliv. ex im Thurn, Timehri 5: 192. 1886.

Myrcia yungasensis'R.xishy, Mem. Torrey C\whS(i): 27. 1893.

Myrcia arimensis Britton, Bull. Torrey Club 48: 334. 1921. Aulomyrcia obtusa var surinamensis (Miq.) Amsh. in Pulle, Fl. Suriname 3(2): 78. 1951. Aulomyrcia obtusa var schomburgkiana (Berg) Amsh. in Pulle, Fl. Suriname 3(2): 79. 1951. .Aulomyrcia roraimae (Oliv.) Steyerm., Fieldiana Bot. 28: 1007. 1957. This plant has passed in recent years under the name of Myrcia (or Aulomyrcia) obtusa in northern South America, and under other names further south. Amshoff (cf Rec. Trav. Bot. Neerl. 4 2 : 21. 1950) studied at the British M u s e u m an Aublet specimen that she took to be the type of Eugenia guianensis, and stated that it represented "a species nearly aUied to Aulomyrcia obtusa." In 1965 I was permitted to confirm this observation on the same specimen and, with the assistance of Miss Hillcoat of the Museum's staff, to section one of the few buds on Aublet's plant. The ovary, as expected, proved to be trilocular. I could find no significant differences between E. guianensis (which incidentally was well illustrated by Aublet), and the common "Aulomyrcia obtusa." The application of the name M . guianensis is not difficult, but more difficult is the circumscription of the taxon to which it applies. As I understand the taxon, it comprises a large series of populations ranging from northern Venezuela and the nearby islands through most of South America east of the Andes to Bolivia and southeastern Brazil. Berg recognized in this group of plants with 3- or 4-locular ovary, which he referred to the genus Aulomyrcia, about 50 species. The actual number of species seems to be much smaller than Berg supposed, but much further work on this complex is needed. In addition to the question of specific limits, there is the even more difficult one of generic limits. The bud in the inclusive Myrcia guianensis is glabrous without, rather long and narrow, acute at base, turbinate or campanulate; the relatively long base is longer than the lobes; the very narrow and elongate bracts are deciduous weh before anthesis; the hypanthium is m u c h prolonged beyond the ovary, prominent and funnel-shaped on the developing fruit when that first begins to expand, collar-like and erect on the fruit until maturity; the calyx-lobes are 5, pubescent on the inner surface, rounded, mostly broader than long, conspicuous and free even in the bud, reflexed in anthesis. As the flower expands and the margins of the hypanthium spread with the reflexing calyx-lobes, short fissures sometimes (but not always) develop between the bases of the lobes, but the lobes are not deciduous, and the distortion of the calyx as a whole is usually almost none. The amount of splitting between the lobes seems to depend partly upon the size of the lobes and partly upon their position at the summit of the hypanthium; that is, if the lobes are small, and if the bud is narrowed toward the tip so that the lobes do not originate at the broadest part, then the pressures in the opening flower usually produce ruptures between the calyx-lobes when these turn back. If on the other hand the lobes are a little larger, and their combined widths approximately equal the circumference of the hypanthium at its widest point, the reflexing of the lobes does not produce unequal stresses but merely accentuates the uniform flaring of the rim of the hypanthium. Berg established the genus Calyptromyrcia on the basis of this very feature, stating as a principal distinction "Alabastra aperta, calyce repando, d e m u m profundius 5-lobo" (as against "Alabastra aperta, calyce 5-sepalo" for Aulomyrcia). I believe the distinction is a specious one. T w o of the species assigned by Berg to Calyptromyrcia, viz, Myrcia elegans D C . and M . spixiana D C , are in m y opinion indistinguishable at the species level from a whole series of plants that Berg assigned to Aulomyrcia, e.g., A. surinamensis, A. schomburgkiana, A. roraimensis, A. cuneata, A. obtusa, and A. poeppigiana. All of these are in m y opinion synonyms of Myrcia guianensis. It is true that in Myrcia (Calyptromyrcia) elegans and M . spixiana the opening flowers split to some extent between the calyx-lobes, but not more so than in many individuals of the various species of "Aulomyrcia." It does not seem that the one variable feature of the splitting calyx, in plants that are otherwise indistinguishable, constitutes a valid generic distinction. There remains the question of whether the members of the M . guianensis complex should be assigned to Myrcia or to Marlierea. The balance seems to favor Myrcia: The ovary is trilocular (as in a rather large number of species of Myrcia but seldom or rarely in undoubted species of Marlierea); the hypanthium after anthesis is little modified, not explanate as often in Marlierea; the calyx-lobes are 5 (as in most species of Myrcia, not 4 which is the more usual number in Marlierea). and weh-formed in the bud, thus hardly at ah torn or modified in anthesis (a Myrcia character); the pubescence is prevailingly of basifixed hairs (as in Myrcia), but at least a few unequally branched hairs can usually be found on a specimen (as in Marlierea); the outer margin of the hypanthium is sometimes but not always ruptured in anthesis (as in Marlierea); the bracts and bracteoles are deciduous before anthesis (as in Myrcia), and the general morphology of the inflorescence is more like Myrcia than Marlierea. M y own decision, on the basis of the above facts, has been to retain this species in Myrcia, sect Armeriela, admitting that the decision is a somewhat arbitrary one. The inclusive Myrcia guianensis is a species with small lustrous and coriaceous leaves usuahy 5-6 cm long but sometimes up to 10 cm long; the midvein is flat or convex above; the herbage and inflorescence are usually somewhat pubescent with straight appressed and partly unequally dibrachiate pale reddish hairs; the buds are described above; for additional description see Amshoff (Fl. Suriname 3(2): 77. 1951, under Aulomyrcia obtusa). There appear to be some recognizable regional populations, but they are difficult to separate except by some rather subjective features of leaf-shape, leaf-size, and density of pubescence. Perhaps the most distinct of these local taxa is the following: