A D I R E C T I O N A L C L I N E IN M O U R I R I G U I A N E N S I S ( M E L A S T O M A T ACE A E )
Thomas M o r l e y ( ; t)
A b s t r a c t
M o r p h o l o g i c a l v a r i a t i o n in M o u r i r i guia-nensis is described and a n a l y z e d t h r o u g h o u t its range in Brazil and adjacent regions. F e a t u res that vary are ovary size, locule and ovule number, shape and smoothness of the leaf blade and petiole length. T h e largest ovaries w i t h the most ovules occur in west central A m a z o n i a ; intermediate sizes and numbers are widespread but reach t h e coast o n l y b e t w e e n M a r a j ó and Ceará; and t h e smallest ovaries w i t h the fewest locules and ovules are coastal or nearcoastal from D e l t a A m a c u r o in V e n e z u e l a to M a r a j ó . Small ovaries also occur in coastal Alagoas and at Rio de Janeiro. Ovaries w i t h t h e fewest locu les and ovules are believed t o be the most specialized, t h e result of e v o l u t i o n t o w a r d decreased waste of ovules, since t h e fruits of all members are few-seeded. Leaf characters correlate statistically w i t h ovule n u m b e r s . Possible origen of t h e d i s t r i b u t i o n p a t t e r n of the species is c o m p a r e d in terms of present rainfall patterns and in terms of Pleistocene climatic change w i t h associated forest refuges. It is concluded t h a t b o t h p h e n o m e n a w e r e probably i n f l u e n t i a l . High specialization appe ars to have a c c o m p a n i e d isolation, for reasons that are unclear. Because t h e plants f r o m D e l t a Amacuro t o Marajó are the most specialized they m a y once have been m o r e isolated t h a n now.
I N T R O D U C T I O N
M o u r i r i guianensis is a small some times shrub-like tree o f t h e neotropics. Its d i s t r i b u t i o n lies across Brazil and extends t o Venezuela on the n o r t h and t o
Rio de Janeiro o n the south (Fig. 10). Certain characteristics o f t h e plants are highly variable over this range; t h e varia tion is examined here t o see t o w h a t extent it may correlate w i t h t h e geogra phic d i s t r i b u t i o n . A n unusual feature o f the present example is t h a t t h e d i r e c t i o n
of specialization of the most i m p o r t a n t variable, t h e ovary, can be clearly identi f i e d . T h e overall pattern of d i s t r i b u t i o n was b r i e f l y described previously (Morley, 1975, 1976); the present paper is a detai led report.
M A T E R I A L A N D M E T H O D S T h e study was carried o u t w i t h pressed specimens b o r r o w e d f r o m many herbaria, t o whose curators I am grateful. The most instructive characters are those o f t h e unripened ovary, and therefoie o n l y f l o w e r i n g material was of value in m o s t cases. It was necessary that speci mens have a considerable excess of flo wers f o r the dissections t o be made w i t h o u t h a r m b u t f o r t u n a t e l y only a few collections had t o be o m i t t e d for this reason. In a f e w critical f r u i t i n g collec t i o n s leaf measurements alone were recor ded. The omission o f most f r u i t i n g collections f r o m Fig. 10 does not materi ally affect the d i s t r i b u t i o n shown, partly because most collections o f the species are o f f l o w e r i n g plants, partly because by good f o r t u n e most o f t h e f r u i t i n g collec tions are f r o m localities where f l o w e r i n g material has also been taken or f r o m places nearby. No i m p o r t a n t range exten sions are o m i t t e d . Coverage o f the collec t i o n s I believe t o be adequate for the
purposes of this paper, b u t there are many gaps w h i c h will probably be filled i n t h e f u t u r e .
T h e relevant floral features are tho se o f ovary size and shape (Fig. 3-9) and the inner components t h a t affect those characters. The diameter o f the dried ( * ) B o t a n y D e p a r t m e n t , University of M i n n e s o t a , S t . Paul, M i n n e s o t a , U S A 5 5 1 0 8 .
ovary can be used as one parameter; however, outside measurements o f t h e tapering and o f t e n d i s t o r t e d ovaries are n o t always reliable. T h e ovary size is a reflection of the n u m b e r o f ovules w i t h i n , and t o a lesser e x t e n t o f t h e n u m b e r and thickness o f t h e p a r t i t i o n s . Consequently the numbers o f locules and ovules have been mapped as t h e major variables o f t h e ovary.
Material p e r m i t t i n g , three t o five flowers were dissected f o r each o f t h e 71 collections examined and occasionally more. L i m i t a t i o n s o f material precluded larger samples. In most cases the range o f variation encountered in a given collec t i o n was n o t great w i t h these small sam ple numbers, leading me t o believe t h a t the results are reasonably representative. The consistency o f counts o f d i f f e r e n t collections f r o m t h e same locality and t h e consistency o f t h e patterns shown i n Fig. 10 s u p p o r t t h e o p i n i o n t h a t the results are adequate f o r use.
The leaves also vary w i t h geography. Blade shape is t h e most consistent varia ble t h a t is readily measured, and t h e w i d t h o f the basal angle is t h e m o s t c o n sistent character o f t h e shape. As t h e an gle becomes narrower, the leaves t e n d t o
become more elliptic and less ovate, b u t this does n o t always h o l d . The possibility that the leaves o n a particular specimen do n o t represent a n o r m f o r t h a t p l a n t is a p r o b l e m t h a t c a n n o t be avoided.
Leaf v a r i a t i o n o n t h e same speci m e n is o f t e n considerable. T h e leaf-bea ring twigs g r o w in spurts or flushes, w i t h resting periods between. T h e lowest lea ves o f each g r o w t h flush tend t o have t h e widest included basal angles, the upper the narrowest (Figs. 1 „ 2). T h e difference may be very slight. When there is b u t a single pair o f leaves on a t w i g , its leaves are most o f t e n like those o f t h e lowest leaves or sometimes the m i d d l e leaves of twigs w i t h several pairs. T h e average angle is used here t o express this leaf character.
When t h e leaves are f o l d e d lengthwise no reliable angle can be o b t a i n e d . When all are loose in a p o c k e t an average angle can o f course be o b t a i n e d b u t there is no c e r t a i n t y t h a t t h e lowest and uppermost f o r m s are present. Averages range from 790 t o 160O; the smallest and largest individual angles measured were 6 1 ° and 1 8 0 ° . T h e basal angle is shown in Fig. 10 as a c o n t i n u o u s variable.
Petiole lenght is also variable and has been mapped. The length ranges from 1 t o 5 m m , and t h e averages o f t h e collec tions vary f r o m 1.5 t o 4 m m . In this ins tance a two-state presentation seemed all t h a t c o u l d be j u s t i f i e d ; a bar o n t h e dia gram in Fig. 10 indicates a petiole average greater t h a n 2.5 m m .
T h e prominence o f t h e lateral nerves in dried leaves is also greater in so me areas t h a n others and is mapped, although sometimes highly variable and d i f f i c u l t t o measure consistently, only a visual estimate being practical. T h e dried leaf surface was rated o n a scale o f 1—5, f r o m veiny t o s m o o t h , using a standard veiny c o l l e c t i o n ( M o r l e y 1164) and a s m o o t h surface as reference p o i n t s . In this case also o n l y a two-state presenta t i o n is given i n Fig. 10. A bar on the diagram indicates a smoothness rating of greater t h a n 3.
The shoots o f these plants are of t w o types, leader shoots and dorsiventral ones, and leaves o f the t w o are dissimilar. The relatively f e w leaders, w h i c h grow u p w a r d w i t h great vigor, bear unusually short leaves w h i c h are o f t e n cordate at base, w h i l e t h e m u c h more common dorsiventral shoots produce t h e typical leaves o f t h e plant. Only t h e typical leaves are referred t o in this paper.
R E S U L T S
E x a m i n a t i o n o f t h e distribution map (Fig. 10) shows the f o l l o w i n g points o f significance:
1. Locule number.
A. This varies f r o m 5 (rarely 6) t o one. Plants w i t h 5 and 4 locules are very^ widespread.
B. The smallest locule numbers occur f r o m coastal Delta A m a c u -ro t o the south side o f Marajó. A l l those ovaries w i t h 2.5 o r fewer locules occur here, and none here have more t h a n 3 ex cept f o r the c o l l e c t i o n at t h e
northeast t i p o f Marajó.
C The coastal and near-coastal collections in Alagoas and Rio de Janeiro have relatively l o w locule numbers. The 2.6 that occurs on the upper Rio Bran co is exceptional, by far the smallest number in the interior. 2. Ovule number.
A. This correlates w i t h locule num ber, w i t h some variation. Five
3 4 5 6 7 8 9
Figs. 1 , 2. Leafy twigs illustrating variation in shape o f leaf blade f r o m plant t o plant and f r o m lower t o upper leaves in a g r o w t h flush. Tracings. 1. Moore 437. 2. Broadway 275. Figs. 3—9. I n f e r i o r ovary and calyx o f d i f f e r e n t flowers
illustrating variation in size and shape o f the ovary in dried flowers. Camera luci-da. 3. Ule 5915. 4. Level 118. 5. K u b i t z k i 7 5 - 7 9 . 6. Weddell 2 4 9 4 . 7. Froes
locules are usually associated w i t h 15 or more ovules, never less t h a n 1 1 . The smallest ovule numbers occur o n l y in ovaries w i t h 1 or 2 locules.
B. The greatest number of ovules occurs in west central Amazonia. The largest number counted
was 3 3 , f o r t h e plant w i t h an average of 2 9 . 3 . T h e numbers decrease t o the n o r t h , east, and south f r o m here. A n area o f moderately high numbers occurs along the A m a z o n in Pará C. Highintermediate ovule n u m
-bers of about 20 occur in wes-tern Venezuela, southwest Ama-zonia, t w o places northwest of Brasilia, and at one site in inner Maranhão. None are on or near the coast.
D. Low-intermediate numbers of about 12-15 are widespread, and extend t o t h e coast between Ma-rajó and Ceará. This is the o n l y part of the coast occupied by plants o f intermediate numbers. E. A group o f six similar collections
is f o u n d in west-central Mato Grosso. The similarity in locule and ovule numbers is emphasi-zed b y generally similar leaf cha-racters.
F. The l o w ovule numbers o f 7-9 are all coastal or near-coastal, occurring between Delta A m a c u -ro and Marajó. In this respect t h e y coincide w i t h the l o w locule numbers mentioned above and w i t h the small sizes mentioned below. No ovule numbers here are greater t h a n 11.3 except f o r the c o l l e c t i o n at the northeast t i p of Marajó. The 10's and 11 's are all f r o m the Paramaribo area. The smallest individual number counted was 6 , f o r t h e Surinam c o l l e c t i o n w i t h an ave-rage o f 7.3.
G.The o n l y other occurrences of 10's and 11's below 11.5 are also coastal or nearly so, one in Alagoas and t w o at Rio de Janeiro. The exceptional colle-c t i o n f r o m t h e upper Rio Brancolle-co w i t h 11.6 ovules (referred to in p o i n t 1D) is the inland collection closest in number t o any of these: five o f its flowers yielded ovule counts f r o m 10 t o 13. 3. Ovary diameter: the fewer the
ovules and locules, the smaller the ovary. Size differences are slight b u t rather consistent. Thus t h e largest ovaries are found in western Amazonia and the smal-lest ones on or near the coast f r o m Georgetown t o Amapá. All ovaries less t h a n 1.2 m m in dia-meter occur in the latter area, none are 1.3 m m or greater, and o n l y t w o measured 1.2 and
1.25 m m . The coastal collection in Delta A m a c u r o has a small locule and ovule number but measured 1.3 m m as did the col-lection o n the south side of Marajó. No inland collections had d r y ovaries measuring less t h a n 1.2 m m .
4. Leaf characters: these are highly variable, b u t some correlations w i t h d i s t r i b u t i o n do exist.
Near-ly all t h e coastal plants, from Delta A m a c u r o t o Rio de Janei-ro, have broad t o moderately broad basal angles, short petioles and veiny leaves, while plants of the interior t e n d t o have the opposite conditions. A n abstract factor t o express these condi-tions can be made f o r each col-lection b y m u l t i p l y i n g t h e avera-ge petiole length by t h e inverse o f t h e blade angle by t h e leaf surface rating b y 100. The coas-tal plants have relatively low factors and t h e inland ones
rela-t i v e l y high f a c rela-t o r s ; when rela-t h e rela-t w o are c o m p a r e d as groups t h e dif ference is highly significant (F test, P = < .001). T h e same re sult is reached using o n l y t h e blade angles. The coastal plants f r o m Delta A m a c u r o t o A m a p á have slightly lower factors t h a n those f r o m Marajó t o Ceará b u t this difference is not statistically significant. When t h e leaf factors are tested f o r c o r r e l a t i o n w i t h ovule numbers t h e result is also highly significant (P » < . 0 0 1 ) , t h e high factors correlating w i t h high ovule numbers. T h r o u g h o u t most o f t h e i n t e r i o r t h e leaf cha racters are q u i t e variable, b u t t w o centers o f long petioles, l o w basal angles, and s m o o t h surfa ces can be seen in Fig. 10, one along t h e lower A m a z o n and t h e other in Mato Grosso.
5. V e r y f e w collections have been made in the central A m a z o n ba sin except along t h e A m a z o n itself. Whether this presents a t r u e p i c t u r e or results f r o m i n c o m p l e t e c o l l e c t i n g is u n k n o w n . In order t o determine i f t h e species might be composed o f t w o or more t a x o -nomic groups, frequency histograms were made o f t h e single most reliable character ovule number ( F i g . 11). One diagram ( A ) uses o n l y the average numbers p l o t t e d in
Fig. 10, while t h e other (B) uses all i n d i vidual counts. In A one sees a grouping o f flowers w i t h 7—9 ovules w h i c h is so dis tinct t h a t one m i g h t t h i n k i t indicates a taxonomic u n i t (see p o i n t 2 F above). Ho wever, i n B it is seen t h a t t h e gap between 9 and 11 ovules rs bridged by m a n y i n d i vidual f l o w e r f r o m plants w i t h average numbers other t h a n 10. This suggests at least t h a t t h e gap is n o t as sharp as the averages make it appear. There is another factor t h a t p a r t l y explains t h e groupings seen in A . T h e ovules t e n d t o be t h e same number o n each placenta; usually there is
a single placenta i n a locule. The t o t a l for the ovary w i l l be the p r o d u c t o f locule number times t h e average number o f ovu les per locule (Table I). The total n u m bers o f 2 0 and 2 0 , 16 and 15, 12 and 12, and 9 and 8 are closer t o each other than t o adjoining numbers and w o u l d create peaks i n a histogram much like those actually f o u n d in Figs. 1 1 A and 11B. The 2 0 - 2 0 peak shows o n l y i n 11B. In 11 A , o n l y t h e peak at 14 is o u t o f place. Con sequently, although the few-ovuled coas tal plants have developed more or less recognizable features, t h e y d o n o t appear s u f f i c i e n t l y distinct as groups t o warrant t a x o n o m i c status.
F r o m a purely morphological p o i n t o f v i e w i t is n o t e w o r t h y t h a t the placen-t a placen-t i o n in cerplacen-tain collecplacen-tions w i placen-t h high ovule numbers ( A p p u n 1 7 1 1 , K r u k o f f 6 6 1 3 , Level 118, Prance & Silva 5 9 3 2 1 , Ule 59T5) resembles in part that o f seve ral species o f Mouriri in w h i c h the ovules are borne o n all sides o f each placenta. In the collections named the ovules are often arranged in a f u l l circle at the apex o f t h e placenta, b u t spread apart t o pass on each side o f i t part way t o w a r d t h e base.
D I S C U S S I O N
The overall d i s t r i b u t i o n pattern is one in w h i c h flowers w i t h the largest ovaries and the most ovules occur in west central A m a z o n i a w h i l e t h e smallest ova
ries w i t h the fewest locules and ovules are coastal or near-coastal f r o m Delta Amacu
ro t o the south side o f Marajó, w i t h t w o other localities of small ovaries in coastal Alagoas and at R i o de Janeiro.
Considering w h a t is k n o w n o f the phylogeny o f the genus (Morley, 1953, 1976) there can be n o d o u b t t h a t the 5—loculed c o n d i t i o n is p r i m i t i v e for the species and t h a t the lower numbers o f locules and ovules represent progressive reduction. T h e more p r i m i t i v e members o f t h e subgenus Mouriri, t o w h i c h M.
7 -;V • d i a m e t e r of d r y o v a r y , 2 m m in this e x a m p l e . • a v e r a g e no. of l o c u l e s - a v e r a g e n o . of o v u l e s - p e t i o l e s r e l a t i v e l y l o n g - b a s a l a n g l e of l e a f b l a d e n a r r o w - l e a f s u r f a c e r e l a t i v e l y s m o o t h
Fig. 10. D i s t r i b u t i o n o f M. guianensis showing geographic variation o f selected f l o w e r and leaf characters. See legend. A bar is shown when t h e petioles are mo re than 2.5 m m long, and w h e n t h e leaf surface is smoother t h a n the median on a smoothness scale. Included angles o f leaf bases range f r o m 7 9 ° (narrow) t o 160° (wide). See Materials and methods.
guianensis belongs, have 15—30 ovules per ovary and i t therefore appears reaso nable t o suppose these numbers t o be primitive f o r M. guianensis. Therefore according t o the present d i s t r i b u t i o n the most p r i m i t i v e members of t h e species are those of western Amazonia and t h e most specialized ones are the coastal and near-coastal ones w i t h small ovaries and f e w locules and ovules. T h e species appears to have originated in the west and migra ted n o r t h , east and south f r o m there.
A n adaptive value can be rationali zed f o r the more specialized forms. A l l known fruits of t h e species are small and contain one or t w o or at most three seeds. Small few-seeded fruits are f o u n d
in t h e most widespread species o f the tribe Memecyleae and appear t o be advantageous f o r b i r d dispersal (Morley,
1975 p. 19). Since so few seeds are pro duced, many ovules must abort when a large number is present before fertiliza t i o n . One m i g h t therefore expect a reduc t i o n series i n . ovule number t o occur in the interests of greater efficiency.
However, i t is n o t clear w h y this reduction should have been accelerated more in some areas than in others. One can only speculate that unk vn compe t i t i v e forces were greater in tne areas of reduction. Because those areas are all rela tively small at present and may have been smaller in t h e past it is possible t h a t
de-6 7 8 9 10 11 12 13 14 15 1de-6 17 18 19 20 21 22 23 24 25 2de-6 27 28 29 30 31 32 33 n o . o f o v u l e s
Fig. 1 1 . Frequency histograms o f ovule numbers in M. guianensis. A. Frequencies of the averages f r o m Fig. 10 as read t o the nearest w h o l e number, e. g. a number f r o m 13.6 t o 14.5 is c o u n t e d as 14. B. Frequencies o f all individual counts me-de. The same number o f counts c o u l d n o t always be made f o r each c o l l e c t i o n ; see Materials and methods, and Results.
creased p o p u l a t i o n size w i t h its m o d i f i e d e v o l u t i o n a r y forces may have been one factor in p r o m o t i n g the r e d u c t i o n . Diffe ring dispersal agents and other altered environmental c o n d i t i o n s m i g h t also have played a part.
T h e association o f leaf characters w i t h ovule numbers ( p o i n t 4 above) sug gests t h a t leaves w i t h long petioles, nar r o w basal angles, and s m o o t h surfaces may be p r i m i t i v e f o r t h e species.
In seeking an explanation o f the d i s t r i b u t i o n pattern o f t h e species, we should first consider whether i t m i g h t have developed under present environ mental conditions. If so, the d i s t r i b u t i o n o f the variables in t h e species should match present environmental zones reasonably w e l l . Rainfall is the factor most easily compared, although even f o r it t h e i n f o r m a t i o n available is incomplete
(Fig. 12). If one excludes the plants of I Alagoas and Rio de Janeiro, there is some correlation o f d i s t r i b u t i o n w i t h precipita-, t i o n t o t h e e x t e n t t h a t t h e largest ovaries and the smallest ones b o t h occur in areas o f high r a i n f a l l , one inland, the other coastal. T h e intermediate sizes and num
bers occupy a w i d e range o f rainfall zones b u t the ones t h a t reach the coast, from
Para t o Ceara, are m o s t l y in a region of lower rainfall. T h e Alagoas collection correlates w i t h an isolated pocket of rela t i v e l y high rainfall and a very short dry season (Prance, 1978). O n l y the Rio de
Janeiro site appears t o have n o relation to
a zone o f higher p r e c i p i t a t i o n and here
t h e d r y season is n o t very pronounced, probably a relevant factor. Both the Ala goas and Rio de Janeiro sites are in a nar r o w coastal strip o f " m o i s t " forest which extends n o r t h f r o m Santa Catarina to Rio Grande d o N o r t e ( M o r i at al, 1981).
Table I
Locule and ovule numbers in M. guianensis T h e average number o f ovules per locule may vary f r o m f l o w e r t o f l o w e r and f r o m c o l l e c t i o n t o c o l l e c t i o n , resulting in diffe rent t o t a l numbers o f ovules in ovaries t h a t may have t h e same numbers of locu les. Some t o t a l numbers are closer t o each other t h a n t o others: 20 and 20, 16 and 15, 12 and 12, 9 and 8. These groupings m a y p a r t l y account f o r some o f the peaks seen in Fig. 11. See Results.
Average Average
no. o f no. o f
ovules T o t a l ovules Total
N o . o f per no. o f No. o f per no. of
locules locule ovules locules locule ovules
(or (or per (or (or per
placentas) placenta) ovary placentas) placenta) ovary
5 6 30 4 3 12 5 5 25 3 4 12 5 4 20 3 3 9 5 3 15 2 or 1 4 8 4 5 20 2 or 1 3 6 4 4 16 ( 1 locule always contains 2 placentas)
Fig. 12. A p p r o x i m a t e annual precipitation in meters in t h e range of M. guianen-sis, redrawn f r o m Ratisbona (1976) and Snow (1976).
A broad relatively d r y zone o f less than 2 m o f rainfall extends f r o m sou theast Brazil northwest across the Ama zon and p a r t l y separates t h e w e t coastal strip between Delta A m a c u r o and Marajó from the wet interior. The b u l k o f this dry arm northwest o f t h e A m a z o n is shown by B r o w n (1982) as having a pro nounced d r y season o f f r o m 3—5 months.
The d i s t r i b u t i o n o f the plants w i
t h i n the wet coastal strip just mentioned is also correlated w i t h rainfall t o a mode rate degree. A close comparison o f Figs. 10 and 12 shows a very close correlation at t h e Delta, while southeast along the coast the c o l l e c t i o n f r o m sites w i t h 2.5 m o f rain or more tend t o have fewer locules and ovules t h a n those f r o m slightly drier areas. Thus it c^n be said that there is a d e f i n i t e b u t imperfect relation between
present rainfall patterns and d i s t r i b u t i o n o f the d i f f e r e n t forms o f M o u r i r i guianen sis.
The very high water table o f most of Delta A m a c u r o m i g h t lead one t o sus pect a relation between this c o n d i t i o n and the plants w i t h few ovules. However, in French Guiana similar plants g r o w at the edges o f savannas w h i c h are relatively d r y according t o Granville (1982).
Nor does the available i n f o r m a t i o n on soils and other environmental factors appear t o coincide w i t h t h e d i s t r i b u t i o n o f the species.
The fact t h a t the plants along the coast have leaves w i t h relatively short pe tioles, broad basal angles, and veiny surfa ces ( p o i n t 4 above) suggests a relation between these forms and maritime i n f l u ences; the adaptive value o f such forms if any is u n k n o w n .
If the species diversified under present c o n d i t i o n s , one w o u l d hypothesi ze its history about as f o l l o w s : moderate r e d u c t i o n o f the ovary tended t o occur as the plants spread n o r t h , east, and south f r o m the p o i n t o f origin in the west, per haps in relation t o environmental gradi ents, b u t this is not clear. Isolation does not appear t o have been a major factor in this development. Plants w i t h modera te reduction carried t o the coast between
Marajó and Ceará. However, when the plants penetrated the broad d r y zone mentioned above and reached t h e coast between Delta A m a c u r o and Amapá and-became adapted to coastal c o n d i t i o n s there, a sufficient degree of isolation exis ted in this case t o p e r m i t accelerated e v o l u t i o n under present conditions. Par tial isolation or t h e existence o f environ mental gradients may p e r m i t such d i f f e r e n t i a t i o n (Benson, 1982, Endler, 1982).
Long distance dispersal w o u l d have brought the plants t o Alagoas and Rio' de Janeiro, where t h e y were well isolated and where accelerated e v o l u t i o n appears t o have taken place. Being bird-dispersed.
the plants presumably have high mobility. Bird m i g r a t i o n routes c o u l d have beene factor.
However, t h e degree o f reduction seen in the plants f r o m Delta Amacuro to Amapá is very sharp and may have been produced under c o n d i t i o n s of greater iso lation t h a n n o w appear t o exist, especially considering t h a t a similar but slightly lesser reduction t o o k place apparently under nearly complete isola t i o n at Alagoas and Rio de Janeiro. The refore it is possible that t h e observed differences are at least partly the result o f past c l i m a t i c changes w h i c h involved t o some e x t e n t the various Pleistocene forest refuges that have been proposed as centers o f forest c o n t r a c t i o n and ex pansion during these changes. The subject is reviewed by Simpson & Haffer (1978). Some correlations exist: (1) t h e plant w i t h the most ovules, in western Amazo nia, is close t o one o f Prances (1982) re-1 fuges although n o t w i t h i n it. (2) The Alagoas location is w i t h i n or very close t o the proposed forest dispersal centers f o r numerous vertebrates (Muller, 1973) and several genera o f butterflies (Lamas, 1973, n. v., i l l . in Simpson & Haffer, 1978). This site is also at the southern tip o f the Pernambuco endemic center for forest butterflies as shown by Brown ( 1 9 7 7 , 1982). (3) T h e Rio de Janeiro location is recognized as a probable forest refuge on t h e basis of neotropical bird d i s t r i b u t i o n (Haffer, 1974), nymphalid butterflies ( B r o w n , 1977, 1 9 8 2 ) , nume rous vertebrates (Muller, 1973), and trees ( M o r i e t a l , 1 9 8 1 ) .
The coastal strip f r o m Delta Ama curo t o A m a p á in w h i c h occur so many plants w i t h reduced flowers finds no close c o u n t e r p a r t in the proposed refuges.
However, Muller (1S73) and Ab'Saber (1982) indicate a large inland arboreal dispersal center nearby t h a t extends from just south of the O r i n o c o delta through most o f A m a p á , avoiding t h e coast except just n o r t h w e s t o f Georgetown. Prance
shows t w o smaller refuges farther inland in the same general area, and B r o w n shows a part o f Amapá as a refuge.
If c l i m a t i c change involving refuges was a major factor in t h e m o d i f i c a t i o n o f the species, then its history m i g h t have been as f o l l o w s : during a Pleistocene d r y period the broad relatively d r y zone of less than 2 m rainfall t h a t extends f r o m southeast Brazil across t h e A m a z o n t o t h e northwest became drier and expanded, dividing the p o p u l a t i o n i n t o f o u r groups of different sizes-the plants t o the west, those c r o w d e d along the northeast coast From Delta A m a c u r o t o A m a p á , and those in Alagoas and Rio de Janeiro. T h e plants trapped along the northeast coast followed t h e moist zones; if the present rainfall pattern is relevant t h e y w o u l d have been squeezed i n t o a small area i n eastern French Guiana and nearby A m a p á with possibly a second group in Guyana. During the Flandrian transgression t h e y would have been forced i n l a n d , very likely t o the a p p r o x i m a t e areas proposed as refuges by Ab'Saber, B r o w n , and Prance. The transgression w o u l d also have driven plants f r o m the area of the A t l a n t i c embayment t h a t m i g h t otherwise have persisted along the main watercourses. For reasons t h a t are unclear b u t w h i c h may have been related t o small popula-tion size, the coastal plants evolved rapi-dly in the d i r e c t i o n o f smaller ovaries with fewer ovules; reproductive barriers seem n o t t o have been f o r m e d judging b y the series o f transitional f o r m s , b u t this has n o t been tested. The plants o n t h e west remained relatively unchanged.
When c l i m a t i c c o n d i t i o n s shifted toward those o f t o d a y , t h e plants spread into all suitable habitats, o c c u p y i n g m u c h of the t e r r i t o r y between t h e f o u r restric-ted zones i n c l u d i n g t h e coast between Marajó and Ceará. Plants w i t h i n the f o u r zones tended t o keep their original cha-racteristics, b u t the migrants developed more or less intermediate traits, possibly due t o h y b r i d i z a t i o n .
The Alagoas and Rio de Janeiro colo-nies remain isolated, b u t some of the plants o f the northeast coast are n o w close t o plants o f the interior and it is here t h a t any h y b r i d i z a t i o n and thus "secondary c o n t a c t " w o u l d have taken place.
In fact it does not appear necessary t o choose one o f the above hypotheses t o t h e exclusion o f the other. It seems probable that b o t h were operative. The evidence for c l i m a t i c change is strong, b u t the changes w o u l d have been o f varying degrees and w o u l d have produced d i f f e r e n t effects in d i f f e r e n t places de-pending on variables such as r a i n f a l l , soil, water table, and w i n d patterns. In some areas present isolation is already so
com-plete t h a t lessened p r e c i p i t a t i o n probably w o u l d n o t increase appreciably the likeli-h o o d o f d i f f e r e n t i a t i o n occurring. In other areas a moderate decrease in rainfall w o u l d accentuate existing differences and accelerate differentiations already proce-eding at a slower pace under conditions of partial isolation or environmental gra-dients or b o t h . Plants might persist along watercourses and in sheltered places du-ring d r y times. Thus the populations might diminish b u t n o t necessarily disap-pear in the driest zones during dry ds and t h e n m u l t i p l y d u r i n g wetter perio-ds. Changes of this level appear sufficient t o account for much and perhaps all of the d i f f e r e n t i a t i o n f o u n d i n M . guianensis. Perhaps in some areas or f o r other orga-nisms f u l l and drastic climatic shifts w o u l d be necessary t o bring about diffe-r e n t i a t i o n .
A C K N O W L E D G E M E N T
I am grateful t o José R. Nascimento f o r translating the s u m m a r y .
R e s u m o
Variação m o r f o l ó g i c a e m M o u r i r i guiarían s i t é d e s c r i t a e analisada e m relação a sua d i s -tribuição n o Brasil e regiões a d j a c e n t e s .
Carac-terísticas q u e v a r i a m são t a m a n h o d o o v á r i o , n ú m e r o de lóculos e d e óvulos, f o r m a e l i s u r a d a f o l h a seca, e c o m p r i m e n t o d o p e c í o l o . O s m a i o r e s ovários c o m o m a i o r n ú m e r o d e óvulos o c o r r e m n o c e n t r o o e s t e a m a z ô n i c o ; t a m a n h o s e n ú m e r o s i n t e r m e d i á r i o s estão d i s t r i b u í d o s l a r g a m e n t e mas a l c a n ç a m a c o s t a m a -r í t i m a s o m e n t e e n t -r e a i l h a i de M a -r a j ó e Ceará; e os m e n o r e s ovários c o m o s m e n o r e s n ú -m e r o s d e lóculos e óvulos e n c o n t r a -m - s e na c o s t a o u p r ó x i m o da c o s t a e n t r e o D e l t a A m a -c u r o na V e n e z u e l a e M a r a j ó . P e q u e n o s ovários t a m b é m o c o r r e m nas costas de A l a g o a s e R i o d e J a n e i r o . A c r e d i t a s e q u e ovários c o m o m e -n o r -n ú m e r o d e óvulos e lóculos são os m a i s es-p e c i a l i z a d o s , r e s u l t a d o da evolução e m direção
à d i m i n u i ç ã o da p e r d a de óvulos, já q u e os f r u t o s de t o d o s os m e m b r o s p o s s u e m p o u c a s s e m e n t e s . F o l h a s c o m r e l a t i v a m e n t e l o n g o s p e c í o l o s , ângulos basais e s t r e i t o s , e superfí-c i e lisa superfí-c o r r e l a superfí-c i o n a m - s e superfí-c o m n ú m e r o g r a n d e de óvulos e p o d e m ser p r i m i t i v o s para a espé-c i e . F o l h a s deste t i p o t i p i f i espé-c a m as p l a n t a s d o i n t e r i o r e n q u a n t o p l a n t a s c o s t e i r a s t e n d e m a t e r f o l h a s c o m condições o p o s t a s . A evidên-c i a é i n s u f i evidên-c i e n t e para s u b d i v i d i r a espéevidên-cie e m d o i s o u m a i s g r u p o s t a x o n ó m i c o s . A possível o r i g e m d o padrão o b s e r v a d o d a d i s t r i b u i ç ã o da espécie é d i s c u t i d o e m t e r m o s (1) d o s p a drões da precipitação a t u a l , e ( 2 ) das m u d a n ças climáticas d o P l e i s t o c e n o e refúgios f l o r e s t a i s associados. C o n c l u i s e q u e a m b o s os f e n ô -m e n o s t e n h a -m p r o v a v e l -m e n t e i n f l u e n c i a d o . A l t a especialização p a r e c e t e r a c o m p a n h a d o i s o l a m e n t o , p o r razões q u e n ã o estão claras. V i s t o q u e as p l a n t a s e n c o n t r a d a s e n t r e o D e l t a A m a c u r o e M a r a j ó são m a i s e s p e c i a l i z a d a s , elas t a l v e z t e n h a m e s t a d o m a i s isoladas n o passado d o q u e observa-se h o j e e m d i a .
References
Ab'Saber, A . N . - 1 9 8 2 . The paleoclimate and paleoecology o f Brazilian A m a -zonia. I n : Prance, G.T. ed. Biological d i v e r s i f i c a t i o n i n t h e tropics. New Y o r k , C o l u m b i a University press, p. 4 1 - 5 9 . Benson, W. W. - 1982. A l t e r n a t i v e mode-ls f o r infrageneric d i v e r s i f i c a t i o n in t h e h u m i d t r o p i c s ; tests w i t h passion vine butterflies. I n : Prance, G. T . ed. Biological d i v e r s i f i c a t i o n in t h e t r o -pics. New Y o r k , C o l u m b i a University press, p. 6 0 8 - 6 4 0 .
B r o w n , K.S. J r . - 1 9 7 7 . Centros de evolu cão, refúgios quaternários e conser-vação de p a t r i m ó n i o s genéticos na re-gião n e o t r o p i c a l : padrões de diferen-ciação em I t h o m i i n a e (Lepidoptera:
Nymphalidae) A c t a Amazonica, 7(1): 7 5 - 1 3 7 .
1982. Paleoecology and regional patterns o f e v o l u t i o n in neotropical forest b u t t e r f l i e s . I n : Prance, G.T. ed Biological d i v e r s i f i c a t i o n in the tropi-cs. New Y o r k , C o l u m b i a University press, p . 2 5 5 - 3 0 8 .
Endler, J . A - 1 9 8 2 . Pleistocene forest refuges: f a t or fancy? I n : Prance, G.T. ed. Biological diversification in the tropics. New Y o r k , Columbia
Uni-versity press, p.641-657.
Granville, J . J . - 1 9 8 2 . Rain forest and xeric flora refuges in Franch Guiana.
I n : Prance, G.T. ed. Biological diver-s i f i c a t i o n i n t h e tropicdiver-s. New York, C o l u m b i a University press, p. 159-1 8 159-1 . Haffer, J.— 1 9 7 4 . A v i a n speciation in tropical S o u t h A m e r i c a . Cambridge, Mass. N u t t a l l O r n i t h o l . C l u b , (14) Lamas, M.G.— 1973. T a x o n o m i a e
evo-lução des géneros I t u n a Doubleday (Danainaee Paititia gen. nov. Thyri-dia H u b n e r e Methena Doubleday ( I t h e m i i n a e ) ( L e p i d o p t e r a , Nympha-lidae). D o c t o r a l Thesis. Univ. São Paulo. Brazil.
M o r i , S.A.; B o o m , B . M . ; Prance, G.T.-1 9 8 G.T.-1 . D i s t r i b u t i o n patterns and conservation o f eastern Brazilian coastal forest tree species. Brittonia, 3 3 : 2 3 3 - 2 4 5 .
M o r l e y , T. —1953. T h e genus Mouriri (Melastomaceae). A sectional revi-sion based on a n a t o m y and morpho-logy. Univ. Calif. Publ. B o t . , 26 : 2 2 3 - 3 1 2 .
1975. The S o u t h A m e r i c a n dis-t r i b u dis-t i o n o f dis-t h e Memecyleae (Melas-tomataceae) in r a l a t i o n t o the Guiana area and t o t h e question o f forest re-fuges in A m a z o n i a . P h y t o l o g i a , 31 :
279-296.
1976. Memecyleae (Melastomata-ceae). Flor. Neotrop., 15: 1 - 2 9 5 . Muller, P.—1973. The dispersal centers of
terrestrail vertebrates in the Neotro-pical Realm. I n : J u n k , W. ed. Biogeo-graphica II. The Hague.
Prance, G.T.—1978. The origin and evolu-t i o n o f evolu-t h e A m a z o n Flora. Inevolu-tercien- Intercien-cia, 3: 2 0 7 - 2 2 2 .
1982. Forest refuges: evidence f r o m w o o d angiosperms. I n : Prance, G.T. ed. Biological diversification in
the tropics. New Y o r k , Columbia University press, p. 137—157.
Ratisbona, L . R . - 1 9 7 6 . The climate of Brazil. I n : Schwedtfeger, W. ed. Climates of Central and South America. New Y o r k , Elsevier, p.219-293.
Simpson, B.B. & Haffer, J . - 1978. Spe-ciation patterns in the Amazonian forest biota. A n n . Rev. Ecol. Syst., 9 : 4 9 7 - 5 1 8 .
Snow, J . W . - 1 9 7 6 . The climate o f nor-t h e r n Sounor-th America. I n : Schwednor-tfe- Schwedtfe-ger. W. ed. Climates o f Central and S o u t h America. New Y o r k , Elsevier, p. 2 9 5 - 4 0 3 .
